Application of a Fourier transform—near infrared reflectance spectroscopy method for the rapid proximate analysis of the greenshell mussel (Perna canaliculus) and king (Chinook) salmon (Oncorhynchus tshawytscha)

Greenshell? mussel (GSM, Perna canaliculus) and king (Chinook) salmon (Oncorhynchus tshawytscha) are New Zealand's two major aquaculture species generating $380 million NZD in exports during the 2017–18 financial year. This study addresses the development and validation of a method based on Fourier transform—near infrared reflectance spectroscopy (FT‐NIRs) to determine proximate composition for both species to aid breeding‐, production‐ and consumer decisions. Rapid measurements of GSM (n = 176) were taken by FT‐NIRs and analysed by traditional wet chemistry ‘reference methods’ to develop calibration models for proximate composition (protein, moisture, fat, ash and carbohydrate). The predictive models for moisture (r² = 0.98, root mean square error of cross validation (RMSECV) = 0.314, residual prediction deviation (RPD = 6.47), protein (r² = 0.91, RMSECV = 0.295, RPD = 3.01)) and carbohydrate (r² = 0.87, RMSECV = 0.440, RPD = 2.78) in GSM performed well. Additional models based on 90 portions of salmon were developed to predict moisture (r² = 0.98, RMSECV = 1.02, RPD = 7), protein (r² = 0.96, RMSECV = 0.347, RPD = 5.08), fat (r² = 0.99, RMSECV = 1.09, RPD = 5.98) and ash (r² = 0.72, RMSECV = 0.05, RPD = 1.9). The predictive FT‐NIRs and reference methods were tested for short‐term and intermediate precision, which demonstrated that the repeatability of the predictive models was comparable to the reference methods. Proximate analysis of GSM and king salmon using FT‐NIRs was quick (minutes for sample preparation and analysis rather than days) and all components were assessed simultaneously. This provides a low‐cost short turn‐around method suitable for industry and research applications.     

Prediction of apparent protein digestibility of ingredients and diets by in vitro pH-stat degree of protein hydrolysis with species-specific enzymes for juvenile Pacific white shrimp Litopenaeus vannamei

Aquafeed production faces global issues related to availability of feed ingredients. Feed manufacturers require greater flexibility in order to develop nutritional and cost-effective formulations that take into account nutrient content and availability of ingredients. The search for appropriate ingredients requires detailed screening of their potential nutritional value and variability at the industrial level. In vitro digestion of feedstuffs by enzymes extracted from the target species has been correlated with apparent protein digestibility (APD) in fish and shrimp species. The present study verified the relationship between APD and in vitro degree of protein hydrolysis (DH) with Litopenaeus vannamei hepatopancreas enzymes in several different ingredients (n = 26): blood meals, casein, corn gluten meal, crab meal, distiller's dried grains with solubles, feather meal, fish meals, gelatin, krill meals, poultry by-product meal, soybean meals, squid meals and wheat gluten. The relationship between APD and DH was further verified in diets formulated with these ingredients at 30% inclusion into a reference diet. APD was determined in vivo (30.1 ± 0.5 °C, 32.2 ± 0.4‰) with juvenile L. vannamei (9 to 12 g) after placement of test ingredients into a reference diet (35 g kg^− 1 CP; 8.03 g kg^− 1 lipid; 2.01 kcal g^− 1) with chromic oxide as the inert marker. In vitro DH was assessed in ingredients and diets with standardized hepatopancreas enzymes extracted from pond-reared shrimp. The DH of ingredients was determined under different assay conditions to check for the most suitable in vitro protocol for APD prediction: different batches of enzyme extracts (HPf5 or HPf6), temperatures (25 or 30 °C) and enzyme activity (azocasein): crude protein ratios (4 U: 80 mg CP or 4 U: 40 mg CP). DH was not affected by ingredient proximate composition. APD was significantly correlated to DH in regressions considering either ingredients or diets. The relationships between APD and DH of the ingredients could be suitably adjusted to a Rational Function (y = (a + bx)/(1 + cx + dx²), n = 26. Best in vitro APD predictions were obtained at 25 °C, 4 U: 80 mg CP both for ingredients (R² = 0.86; P = 0.001) and test diets (R² = 0.96; P = 0.007). The regression model including all 26 ingredients generated higher prediction residuals (i.e., predicted APD − determined APD) for corn gluten meal, feather meal, poultry by-product meal and krill flour. The remaining test ingredients presented mean prediction residuals of 3.5 points. A model including only ingredients with APD > 80% showed higher prediction precision (R² = 0.98; P = 0.000004; n = 20) with average residual of 1.8 points. Predictive models including only ingredients from the same origin (e.g., marine-based, R² = 0.98; P = 0.033) also displayed low residuals. Since in vitro techniques have been usually validated through regressions against in vivo APD, the DH predictive capacity may depend on the consistency of the in vivo methodology. Regressions between APD and DH suggested a close relationship between peptide bond breakage by hepatopancreas digestive proteases and the apparent nitrogen assimilation in shrimp, and this may be a useful tool to provide rapid nutritional information.     

Salinity effects on reproduction of giant freshwater prawn Macrobrachium rosenbergii (de Man)

Understanding the role of salinity in breeding and growth has the potential to enhance production of giant freshwater prawn, Macrobrachium rosenbergii. This study investigated the reproduction of females reared in salinities of 0, 6, 12, and 18 g L^− 1. Mean weight of females decreased with increased salinity (31.40 ± 1.54, 25.14 ± 1.16, 20.80 ± 0.81, and 16.62 ± 1.04 g at 0, 6, 12, and 18 g L^− 1, respectively). Larval production was delayed by 2 months in females reared in 12 g L^− 1 compared to 6 and 0 g L^− 1 and the cumulative number of berried females decreased with increased salinity. The number of larvae produced was positively correlated to weight of female. A larval production not only differed between salinity treatments, but also that larval production per gram of female differed between treatments. Females reared in lower salinity of 0 and 6 g L^− 1 produced larger numbers of larvae (12,155 ± 480 and 6519 ± 323, respectively) compared to 12 and 18 g L^− 1 (3751 ± 256 and 0, respectively). The number of larvae produced per gram of female was inversely related to the salinity levels (Y = − 37.54X + 685.65, n = 339, r² = 0.995, p < 0.05). Survival of larvae from females reared at 0 and 6 g L^− 1 was higher than those from females reared in 12 g L^− 1. This study clearly shows that female broodstock reared in lower salinity was larger, reproduced early, and produced more offspring than at higher salinity and this could significantly impact coastal prawn culture where seasonal fluctuation of salinity in the hatchery is common.     

The effect of temperature on the growth, survival and food consumption of the east coast rock lobster Panulirus homarus rubellus

The successful culture of the east coast rock lobster Panulirus homarus rubellus is reliant, among other factors, on the provision of optimal water quality for growth and survival. This study investigated the effect of temperature over a range of 9.7 °C (18.9 ± 0.7 °C to 28.6 ± 1.5 °C) on the growth and survival of juvenile (40.4 ± 9 mm CL; 63.64 ± 12.05 g) P. h. rubellus fed a diet of fresh mussel flesh. Specific growth rate (SGR) was significantly different between temperatures (p = 0.01), with the highest values recorded for the 24 and 28 °C treatments. There was no significant difference in moult increment (MI) between temperatures in terms of both an increase in weight (p = 0.83) and carapace length (p = 0.54). Intermoult period (IMP) differed significantly between temperatures (p = 0.0015) with mean IMP lowest at 24 °C, although not significantly different from the means of the 26 and 28 °C treatments. IMP was highest at 19 and 21 °C. Apparent feed intake was significantly different between treatments (p < 0.0001) and exhibited a strong positive correlation with increasing temperature (y = − 1.67 + 0.16x ; r² = 0.81). Food conversion ratio (FCR) differed significantly between temperatures (p = 0.02) with 24 °C exhibiting the most efficient FCR. Results indicate that efficient growout of juvenile P. h. rubellus, in terms of both growth and food conversion efficiency, is obtainable at 24 °C.     

Low optimal temperatures for food conversion and growth in the big-headed turtle, Platysternon megacephalum

We held juvenile big-headed turtles, Platysternon megacephalum, from eastern China, at temperatures from 20 to 29.4 °C to determine effects on feeding, growth and food conversion. Food intake increased significantly from 20 to 22.4 °C, remained high until 27.1 °C, and then decreased dramatically at 29.4 °C. Digestive efficiency for energy decreased as temperature increased, whereas the digestive efficiency of protein increased from 20 to 25 °C, and decreased at higher temperatures. The relationships between specific growth rate (SGR), food conversion coefficient (C_c) and temperature (T) were curvilinear, and could be described by quadratic equations: SGR = −0.01 T² + 0.47 T − 5.24 and C_c = −0.37 T² + 17.20 T − 181.85. Maximum growth was estimated to occur at 23.9 °C, with 90% of the maximum being achieved within the range of 21.9–25.8 °C; maximal food conversion occurred at 23.2 °C, with a 90% range from 21.0 to 25.4 °C. The temperature range (22–25 °C) found to promote best growth and food conversion in juvenile P. megacephalum is lower than for many other freshwater turtles. Temperatures of 22–25 °C are recommended for use in culture of this species to maximize growth and food conversion.     

Energy and resource consumption of land-based Atlantic salmon smolt hatcheries in the Pacific Northwest (USA)

This paper evaluates the resource and energy requirements of six different types of land-based, hatchery production systems located in the U.S. Pacific Northwest: flow-through with a gravity water supply, flow-through with a pumped water supply, flow-through with pure oxygen, partial reuse system, partial reuse with heating, and a reuse system for the production of Atlantic salmon (Salmo salar) smolts. Key parameters used in the evaluation include direct energy, indirect energy, transportation energy, greenhouse gas emissions, and pollutant discharges.Power (electricity and natural gas) and feed energy accounted for the majority of the required energy for all the rearing option evaluated. The sum of the fixed capital and chemicals components accounted for less than 2–12% of the total energy budget for any rearing option. The energy efficiency (energy output/energy input) of the six options ranges from 0.97% for flow-through with pumped supply to 3.49% for the flow-through with gravity supply. The rearing options with the three highest energy efficiencies were flow-through with gravity supply (3.49%), partial reuse (2.75%), and reuse (2.64%).On a kg of smolt produced basis, the six rearing options showed a wide range in performance. The reuse system had the lowest water (2 m³ kg^− 1) and land (0.13 m² kg^− 1) requirements and the third lowest total energy requirement (288 MJ kg^− 1). The partial reuse system had the second lowest total power requirement (276 MJ kg^− 1), a low land requirement (0.21 m² kg^− 1), and moderate water requirements (33 m³ kg^− 1). The partial reuse with temperature control had the second highest total power requirement (657 MJ kg^− 1) and land and water requirements similar to the partial reuse system without temperature control. The flow-through system with pumped water supply had the highest water (289 m³ kg^− 1), land (2.19 m² kg^− 1), and energy requirements (786 MJ kg^− 1) of any of the rearing options. By comparison, the flow-through system with gravity water supply had the lowest energy requirement (218 MJ kg^− 1), a moderate land requirement (0.78 m² kg^− 1), and a high water requirement (214 m³ kg^− 1). The ranking of the six rearing options based capital and operating costs are likely to be quite different from those based on energy, water, and greenhouse gas emissions.     

Existence of APGWamide in the testis and its induction of spermiation in Haliotis asinina Linnaeus

Immunolocalization by using rabbit polyclonal antibody against APGWamide demonstrated that there was APGWamide immunoreactivity (APGW-ir) in the varicosed nerve fibers in the capsule, connective tissue and trabeculae of the testis whereas there was no APGW-ir in the ovary of sexually mature broodstocks of Haliotis asinina. In vivo bioassay, by injecting APGWamide into foot muscle of mature males and females (age over 24 months), showed that most males (87.50%) injected with 200 μl of 10^− 3 M APGWamide (170 μg APGWamide/animal) could be induced to spermiate whereas fewer males (43.75%) injected with 200 μl of 10^− 6 M APGWamide (0.17 μg APGWamide/animal) could spermiate. Following injection with 10^− 3 M, 53% of males spawned within 3 to 4 h, while the remaining males spawned within 2 to 3 h. The former tended to release more sperm at the range of 1.04 to 2 × 10⁹, and the latter at the range 3.62 × 10⁷ to 2.07 × 10⁸ cells, respectively, and that the sperm of the former group appeared to be more motile. Following the injection of 10^− 6 M, all inducible males spawned within 2–3 h, and 43% of spawned males have sperm around 2 × 10⁹, while 57% have fewer sperm number ranging from 2.75 × 10⁷ to 9.94 × 10⁸ cells. In contrast to males, none of the mature females with ripen ovary could be induced to ovulate. These data suggest that APGWamide is an important signaling molecule that plays a role in the male reproductive process that could be used to induce spermiation.     

Influence of duration of aeration on growth and survival of carp fingerlings during high density seed rearing

Impact of varied durations of aeration on growth, survival and production performances of catla (Catla catla), rohu (Labeo rohita), fringe lipped carp (Labeo fimbriatus) and olive barb (Puntius sarana) were evaluated in outdoor concrete tanks (10 m × 5 m × 1.3 m) during fingerlings rearing. At a combined stocking density of 0.5 million fry/ha, provision of night time aeration for 4, 8 and 12 h was evaluated as the three treatments, T-I, T-II and T-III, respectively against control (T-c, without aeration). Overall survival and net biomass of the species increased among the treatments significantly as a function of aeration hours (T-c < T-I < T-II < T-III). Aeration for 8 and 12 h showed significantly higher survival, harvested body weight and SGR in all the carps than those with 4 h (T-I) and no aeration (T-c), suggesting 8–12 h of aeration requirement for fingerlings rearing at such high density. Further, no significant difference between survival levels in T-II and T-III groups suggested 8 h of aeration to be adequate. However, while species-wise performance showed 8–12 h night time aeration to be advantageous for catla and rohu, aeration for 4 h was adequate for fringe lipped carp and olive barb.     

Seasonal changes in muscle structure and flesh quality of 0+ and 1+ Atlantic salmon (Salmo salar L.): impact of feeding regime and possible roles of ghrelin

Growth performance, muscle cellularity, flesh quality, and plasma ghrelin were investigated in 0+ and 1+ farmed Atlantic salmon (Salmo salar L.) from 40 g to 4.3 kg. Reduced meal frequency was introduced in both smolt groups from ~1.5 kg; one meal per second day (<5 °C) to one daily meal (>5 °C), while control groups were fed one to three daily meals. Results show that 0+ salmon had higher final fibre number and density, pigment content, red colour intensity, firmer flesh, and lower fillet fat content than 1+ salmon at 4.3 kg, affected by season and smolt type. Muscle fibre recruitment was an important determinant of fillet firmness and colour, possibly influenced by the prenatal temperature regime. Fish fed reduced meal frequency showed temporal reduced feeding ration, but growth performance was not compromised in any smolt groups at harvest. However, fillet fat, gaping, and colour decreased by less frequent feeding, with permanent effects in 1+ salmon for gaping and fat. Reduced meal frequency is therefore considered to be a promising tool for managing important flesh quality attributes in salmon without compromising growth performance. It is also suggested that ghrelin stimulates short‐term appetite, and perhaps also in the longer term.     

High‐oil residue camelina meal,a viable source of protein at low levels in diets for juvenile salmonids

The oilseed Camelina sativa has been studied as a lipid source for farmed salmonids, but recommended inclusion as a protein source has not been determined. This study evaluated low inclusion of camelina high‐oil residue meal (HORM) at 20, 40 and 60 g/kg of the diet, to determine an adequate level for Atlantic salmon parr (Salmo salar) and rainbow trout (Oncorhynchus mykiss). Salmon and trout were fed experimental diets containing up to 60 g/kg HORM for 16 weeks. At 40 g/kg HORM, trout and salmon growth performance were similar to those fed a control diet. However, at 60 g/kg HORM, trout showed lower final weight, weight gain and feed intake than those fed the control diet. Rainbow trout fed 40 and 60 g/kg HORM showed significantly lower whole body ash (p = .005), slightly lower whole body protein levels and higher fat than the control. In salmon fed 60 g/kg HORM diets, whole body ash (p = .024), and the submucosal layer of the intestine was thicker than the control (p = .007). Current results indicate that up to 40 g/kg HORM can be included in diets for rainbow trout and salmon juveniles.     

Reduction of early sexual maturation in male S0 Atlantic salmon (Salmo salar L.) by dietary supplementation of tetradecylthioacetic acid (TTA)

Effects of dietary tetradecylthioacetic fatty acid (TTA) on muscle fat, development of gonads and early sexual maturation in S0 Atlantic salmon during the first year in sea were investigated. TTA (0.5% w/w) was added to the feeds for 8 weeks in the spring. In May, at the end of the TTA‐feeding period, the fish in the TTA group had significantly (P < 0.05) less fat (10.1%) stored in muscle compared with the control group (10.8%). In September, mean male gonadosomatic index (GSI) in maturing fish in the TTA group was found to be lower compared with the maturing fish in the control group (P = 0.05). On the basis of GSI values, male sexual maturation in September was 10.0% vs. 14.4% for the TTA and the control group respectively. Thus, relative to the control group, the incidence of male sexual maturation in the TTA group was reduced by about 1/3 (P = 0.002). Production data was not affected by dietary supplementation of TTA. This study reveals that TTA significantly reduces the incidence of male sexual maturation in S0 Atlantic salmon. A significant elimination model of TTA in fish muscle that takes into account, the growth rate of the fish was further developed in this study.     

Swimming depth and thermal history of individual Atlantic salmon (Salmo salar L.) in production cages under different ambient temperature conditions

Salmon production cages at sites with a pronounced thermal stratification give individual fish an opportunity to choose their thermal environment. The behavioural responses of individual salmon to such stratification, however, are poorly documented. Information about spatial distributions and temperature experience of individual Atlantic salmon (initial weight 1.5 kg) was gathered over a period of 4 months (mid-August to early-December) using data storage tags. Fish were stocked at normal or high densities in triplicate 2000 m³ production cages at 5.6–14.5 (ND) or 15.7–32.1 (HD) kg m^− 3, and valid data were collected for 12 ND and 11 HD salmon. There were large inter- and intra-individual variations in swimming depth, with indications that the salmon performed behavioural thermoregulation in an attempt to maintain body temperature within the range of 8–20 °C. Stocking density influenced the average swimming depth and body temperature, indicating competition for preferred thermal space in periods of unfavourably high temperature (towards 20 °C) in large parts of the cage volume. Analysis of temporal behavioural patterns demonstrated a higher variability during day than night and that 60 to 70% of the individuals displayed cyclic diel patterns in either swimming depth or body temperature in at least one out of three sub-periods. The results are discussed in relation to bio-energetic and thermal stress theory and possible consequences for growth variation in salmon cages. Generally, this study suggests that individual swimming depth and body temperature is in part a response to available temperature interacting with stocking density and time of day, while some individual variation cannot be ascribed to the measured variables.     

Sexing accuracy and indicators of maturation status in captive Murray cod Maccullochella peelii peelii using non-invasive ultrasonic imagery

Macroscopic- and histological-based assessments of gonad condition were compared with ultrasound images to determine the feasibility of this technology as a non-invasive diagnostic tool for identifying sex and assessing maturation status of Murray cod. Four age-classes (1+, 2+, 3+ and 6+ years), were sub-sampled at monthly intervals throughout their annual reproductive cycle and scanned with a 5 MHz linear transducer. An interpretation of sex was made from the resulting images and maximum cross-sectional gonad diameter and area were recorded. Fish were subsequently dissected to confirm gender, and the weights and maturation status of gonads determined and then compared with their respective image profile. Ovaries of females were usually a distinctive feature in ultrasound images, being particularly obvious in older and/or more developed fish. In contrast, the identification of male testis was more problematic. Nonetheless, identifying sex from ultrasound images was consistently achieved by recording the presence/absence of a female ovary (96% total sexing accuracy). Maximum cross-sectional ovary diameter and area were highly correlated with gonad weight (r² = 0.90 and 0.89, respectively) suggesting that indices of maturation status, comparable to the gonadosomatic index (GSI), can be obtained non-destructively from ultrasound scans of females. A less distinct relationship occurred between these dimensions and weight of testes (r² = 0.41). Significant increases (P < 0.05) in mean gonad index (GI, calculated from gonad diameter) occurred for most gonad development stages. However, differences in mean GI between maturation stages were confounded by phenotypic variability, indicating that GI may be limited to population level studies. Nevertheless, ultrasound images of ovaries at each development stage were visually distinctive and enabled qualitative evaluations of maturity, thereby complementing quantitative GI assessments. Repeated serial-monitoring of the same population using ultrasound appears to have great potential for tracking maturation-induced changes in broodfish.     

Effect of light on oxygen consumption and ammonia excretion in Haliotis discus discus, H. gigantea, H. madaka and their hybrids

Oxygen consumption and ammonia excretion rates of three abalone species, Haliotis discus discus, H. gigantea, H. madaka and their hybrids were measured at 20 °C by incubating for 3 h under dark and light (N = 9–13 for each species and hybrid). Animals were fasted before and during the experiment and measurements were made first under dark followed by light on the next day. The rates increased with the increase in body weight and were higher under light than dark. On average, H. discus discus had higher oxygen consumption (DD; dark = 0.039, light = 0.04 ml/g/h) than H. gigantea (G; D = 0.033, L = 0.036) and H. madaka (M; D = 0.034, L = 0.035); the hybrids had varied patterns with respect to their parental species [DD × M (D = 0.032, L = 0.038); M × DD (D = 0.03, L = 0.038); G × DD (D = 0.035, L = 0.04) and DD × G (D = 0.03, L = 0.034), mother first]. M (0.261, 0.298 μmol/g/h) had the highest ammonia excretion rate while G (0.162; 0.264) and DD (0.229; 0.232) had the lowest under dark and light, respectively. The hybrids had varied patterns in comparison with their parents (DD × M = 0.247, 0.32;M × DD= 0.177, 0.28; DD × G = 0.249, 0.364 and G × DD = 0.116, 0.155). The O/N ratios under both conditions in all species and hybrids indicated that they had carbohydrate dominated metabolism. Results demonstrated physiological variability among the species and hybrids indicating necessity of different strategies for their management and aquaculture.     

Long-term separate and combined effects of environmental hypercapnia and hyperoxia in Atlantic salmon (Salmo salar L.) smolts

Atlantic salmon (Salmo salar L.) parr (mean start weight 50 g) were reared in freshwater (FW) and exposed to three levels of oxygen saturation measured in effluent water; control group (93% O₂, LO₂), medium (111% O₂, MO₂) and high (123% O₂, HO₂). Further three groups were exposed to similar water oxygen levels in combination with elevated carbon dioxide levels (17–18 mg L^– 1 CO₂), named LO₂–CO₂, MO₂–CO₂ and HO₂–CO₂, respectively. The experiment was run in duplicate tanks for 42 days, and the fish were subsequently transferred to the same seawater (SW) regime for 45 days for an assessment of post-smolt growth. As a consequence of the CO₂ addition, tank pH levels in the FW period were reduced from 6.7 to 5.9 for the hypercapnia groups compared to for the normcapnia groups. Water temperature in FW ranged between 6.4 and 9.0 °C. Citrate was added to the water to complex labile aluminium.In the CO₂ groups observed ventilation frequencies were significantly increased compared to the control (p < 0.05). This difference declined towards the end of the FW period, suggesting acclimation to elevated CO₂. The degree of oxygenation appeared to contribute to the acclimation as the lowest mean ventilation frequency on day 36 was found in the HO₂–CO₂ group and the highest in the LO₂–CO₂ group. Lower plasma chloride and sodium levels were observed in the CO₂ groups relative to the respective oxygenation groups during the FW period, while plasma chloride and sodium levels were normalised to equal levels for all groups after 44 days in SW. No significant differences were found among treatments for blood concentrations of red blood cells, haemoglobin, potassium and glucose during the experiment.By termination of the FW period, the HO₂ group had significantly higher body weight than all other groups (p < 0.05), with specific growth rate significantly higher than the CO₂ groups (p < 0.05). Further, the condition factor was significantly lower in all the CO₂ groups at the end of the FW period compared to the control and normcapnia groups (p < 0.05). Although variable among replicates, occurrence of nephrocalcinosis was 10 times higher in the hypercapnia groups than in the control and normcapnia groups. Mortality was negligible (< 2.0%) during the trial, and most of the mortality occurred following SW transfer.     

Broad snouted caiman (Caiman latirostris) growth under different rearing densities

The effect of density on growth in body mass (BM) and total length (TL) of Caiman latirostris hatchlings raised in small pens (area 0.36 m²), for 3 months, was investigated. Twelve animals from each of three clutches were randomly distributed (1, 2 or 3 individuals) to two replicates at low rearing density (LRD: 0.12 m²/individual), medium rearing density (MRD: 0.06 m²/individual) and high rearing density (HRD: 0.04 m²/individual. Growth at LRD [BM: 150.75 ± 43.83 g (SE); TL: 11.58 ± 0.93 cm] and MRD (BM: 141.96 ± 22.55 g; TL: 8.38 ± 1.26 cm) was significantly more than at HRD (BM: 57.19 ± 14.38 g; TL: 4.61 ± 0.89 cm; p < 0.001). Density is important to achieving optimal growth and maintaining the well-being of C. latirostris in commercial ranching programs.     

Age and growth of the largemouth perch Percichthys colhuapiensis in the Negro river, Argentine Patagonia

Largemouth perch (Percichthys colhuapiensis) represents one of the most economically important fish species in the Argentine Patagonia. However, little research has been done on the age and growth and population dynamics of this fish, though both studies are essential to properly deal with fisheries forecasts and management. As a contribution to elaborating management programmes for P. colhuapiensis, we evaluated the age and growth of this species in the Negro river via scale and whole otolith reading methods. The sample consisted of 579 specimens ranging in total length (TL) from 90 to 475 mm, captured seasonally from December 1994 to December 1995. The formation of scale annuli (end of winter) and the hyaline zone on otoliths (winter) of adult fish coincided with the beginning of the spawning season (end of winter-beginning of spring). The maximum estimated age was 11 years, which indicates that this is a relatively long-lived species. Otoliths were useful for ageing specimens 1–5 years-old, but above this age whole otoliths yielded lower age estimates than scales. Isometric growth of weight with length was found for total population, juveniles, and separate sexes (p > 0.25 in all cases). No significant differences between the length–weight relationships of sexes were observed (p > 0.10). Length at first maturity was significantly higher for males (TL₅₀ = 271 mm TL; r = 0.88) than for females (TL₅₀ = 243 mm TL; r = 0.96) (p < 0.01). Largemouth perch exhibited a consistent pattern of increase in length with age, with a period of fast growth during the first 5 years, and a slow-growing phase during the rest of his life. The growth parameters based on scale data were L∞: 462.1 mm, k = 0.23 and t₀ = −0.94 for total population, L∞: 402.3 mm, k = 0.33 and t₀ = −0.67 for males, and L∞: 548.4 mm, k = 0.15 and t₀ = −1.59 for females, whereas those based on otolith reading were L∞: 537.4 mm, k = 0.17 and t₀ = −1.0 for total population, L∞: 497.6 mm, k = 0.21 and t₀ = −0.79 for males, and L∞: 582.0 mm, k = 0.14 and t₀ = −1.53 for females. Scales are concluded to be the best structure to age P. colhuapiensis because they rendered L∞ values closer to the maximum TL observed, high precision, easiness of collection, low processing time, and the possibility of performing non-destructive monitoring studies.     

RRR-α-Tocopheryl succinate is a less bioavailable source of vitamin E than all-rac-α-tocopheryl acetate for red drum, Sciaenops ocellatus

Bioavailability of the succinate ester of α-tocopherol has never been investigated with aquatic animals to date. Therefore, a 12-week feeding trial was conducted to compare bioavailability of α-tocopheryl acetate and α-tocopheryl succinate by slope ratio analysis. The semi-purified diets were supplemented with either 0 (basal), 10, 20 and 40 IU vitamin E/kg as all-rac-α-tocopheryl acetate or 10, 20, or 40 IU vitamin E/kg as RRR-α-tocopheryl succinate. Red drum juveniles were conditioned by feeding the basal diet for 8 weeks prior to the experimental period to reduce whole-body tocopherols. Fish initially averaging 12.2 ± 0.4 g/fish (mean ± SD) were fed experimental diets at a rate approaching apparent satiation for 12 weeks. Weight gain and feed efficiency responses of fish fed diets were not significantly altered by the type or level of vitamin E supplemented. However, α-tocopherol levels in liver and plasma were significantly (P < 0.01) influenced by dietary vitamin E level and ester form. The liver retention of α-tocopheryl acetate was 14 times higher than α-tocopheryl succinate, while thiobarbituric acid reactive substances (TBARS) in liver of fish fed α-tocopheryl acetate tended to be (P < 0.1) lower than that of fish fed α-tocopheryl succinate. In addition, plasma ascorbic acid in fish fed graded levels of α-tocopheryl acetate was significantly higher than fish fed graded levels of α-tocopheryl succinate. Fish fed the basal diet and 10 IU α-tocopheryl succinate/kg showed edema in the heart, while fish fed all other diets did not exhibit this pathology. Within the dose range of 0–40 IU/kg diet, hematocrit, neutrophil oxidative radical production and intracellular superoxide anion production of head kidney macrophages were not significantly influenced by α-tocopherol ester or dietary supplementation level. In conclusion, α-tocopheryl succinate is not readily available to juvenile red drum compared to the widely used α-tocopheryl acetate.     

Measures of egg quality in induced spawns of the Asian sea bass, Lates calcarifer Bloch

The egg morphometry and lipid and protein components were determined in induced spawns (n=14) of the sea bass, Lates calcarifer, to identify measures of egg quality. Based on fertilization and hatching rates, the spawns were classified either in Group I, (zero fertilization) or Group II (where fertilization and hatching occurred). The egg morphometry did not differ between the two groups (p > 0.05). The total lipid was higher in Group II than in Group I, although the difference was not significant (p > 0.05). The EPA and linoleic acid were significantly higher in Group II (p < 0.05). There were positive correlations between the total saturated fatty acids and fertilization rate (p < 0.05; r=0.58), the total saturated fatty acids and percentage of normal zygotes (p < 0.02; r=0.62), and DHA and the percentage of normal zygotes (p < 0.04; r=0.56). The total protein and FAAs were higher in Group I than in Group II, but the differences were not significant (p > 0.05). Proline, glycine, p-ethanolamine, and aspartic acid were significantly higher in Group II (p < 0.05), while tyrosine and glutamic acid were significantly higher in Group I (p < 0.05). Phosphoserine and fertilization rate were positively correlated (p < 0.03; r=0.60), as well as aspartic acid and hatching rate (p < 0.05; r=0.54). Arginine was negatively correlated with fertilization rate (p < 0.03; r=–0.61) and the percentage of normal zygotes (p < 0.03; r=–0.63). Serine was inversely correlated with yolk volume of the newly-hatched larvae (p < 0.03; r=–0.77). The moisture content of the eggs, which was significantly higher in Group II than in Group I (p < 0.03), was directly correlated with the FAAs:protein ratio (p < 0.03; r=0.76). The present results reveal egg components that may be used as quality measures in induced spawns of sea bass, a euryhaline teleost that spawn pelagic eggs containing an oil globule.