Effect of stocking density,oxygen level,light regime and swimming velocity on the incidence of sexual maturation in adult Atlantic salmon (Salmo salar)

The effects of various environmental parameters on sexual maturation of two sea-winter Atlantic salmon (Salmo salar) were tested in two separate experiments. In the first experiment Atlantic salmon with initial mean individual weight 1.5 kg (smolt 13 months before) were reared for 8 months from June to February at different oxygen levels and stocking densities using continuous light. Oxygen levels of 5–7, 7.5–9.5 and 10–12 mg O₂ l⁻¹ and stocking densities starting at about 20, 30 and 40 kg m⁻³ and increasing as the fish grew to 80–90 kg m⁻³ for the highest densities were tested in a factorial design. Only male fish matured, and incidence of maturation among males varied from 4.1% to 25% between tanks. The highest percentage of mature males was found in the tanks with low stocking density. No clear effect on oxygen level was found.The second experiment lasted 20 months from seawater transfer in May until the fish weighed 3.3–3.5 kg. Two water current speeds (14–16 and 20–24 cm s⁻¹) and two photoperiod regimes (LD 20:4) and continuous light (LL) were tested in a factorial design. Neither swimming velocity nor photoperiod affected growth rate. Continuous light reduced the incidence of sexual maturation. The average proportion of maturation among males was 8% and 25% under the LL and LD 20:4 regimes respectively. The fish reared under the LD 20:4 light regime had a significant lower condition factor and significant larger hearts than the fish reared under continuous light. Swimming velocity had no significant effect on the incidence of maturation. The results indicate that the swimming velocity must be higher than 0.5 BL s⁻¹ in order to influence the energy stores. An important finding in this study is that light cues are not required for gonadal growth. The results also indicate that environmental factors can affect maturation even after the first sea-winter.     

Influence of photoperiod and temperature manipulation on gonadal development and spawning in Caspian roach (Rutilus rutilus caspicus): Implications for artificial propagation

Caspian roach (Rutilus rutilus caspicus), a spring spawning teleost, were subjected to various photoperiod and temperature regimes to study the feasibility of shifting the timing of spawning for artificial propagation purposes. A total of 650 female reproductively mature R. rutilus caspicus were subjected to different photoperiod and temperature regimes including four light regimes (natural light (NL), 16 hr of light (L):8 hr of darkness (D), 9L:15D, 11L:13D), each affected by three temperature regimes (14, 20 and 24°C) for 70 days. Five fish per tank were randomly sampled on Feb. 10, Feb. 20, March 28, April 15 and April 30 (natural spawning time). Ovarian tissue sections were studied using light microscope and transmission electron microscope (TEM). The levels of 17‐β estradiol (E2) and 17α‐hydroxyprogesterone (OHP) were also measured in the serum samples. In late winter (March 28th), the gonadal maturation and spawning were accelerated in fish treated with the long day length (16L/8D) and warm temperature (20°C). While, the maturation of oocytes and spawning delayed in fish exposed to low temperature (14°C) and short day length (9L/15D and 11L/13D). Photoperiod seems to play a more important role in the ovarian development of the R. rutilus caspicus compared to temperature; since even among the fish treated with the lowest temperature (14°C), those exposed to a longer day length (16L/8D), matured and spawned earlier than the others. Considering that the earliest spawning occurred in R. rutilus caspicus treated with 16L/8D at 20°C and the latest spawning occurred in fish exposed to low temperature and short photoperiod, it can be concluded that temperature and photoperiod play an important role in accelerating oocyte maturation and spawning.     

Long photoperiod delayed spawning and increased somatic growth in gilthead seabream (Sparus aurata)

The effects of extended photoperiods, mimicking the longest day of the year, were studied in 1- and 2-year seabream. The photoperiod regimes started in late July, 36 and 39 days after the summer solstice and continued for 11 months, well beyond the natural reproductive season of December–March. Regime 1 (long day, 15.5L:8.5D), which used natural and fluorescent light, reduced the incidence of maturity in both year classes and females did not spawn although some gonadal development was observed. Among all 1-year sampled fish of regime 1, a maximum of 5% became spermiating males (March) and 5% reached the yolk granule stage of vitellogenesis (VO3; 250–400 μm diameter) by May. Among 2-year sampled fish of regime 1, 45% became spermiating males and 25% were females, which reached the advanced vitellogenesis stage (VO4; 400–600 μm) by April. Regime 2 (skeleton photoperiod), consisting of natural light and a 1.5-h pulse of fluorescent light during the period 14–15.5 h after sunrise, postponed gonadal development and spawning for up to 3 months. In this regime, a maximum of 80% of 1-year sampled fish were spermiating males in February and a maximum of 10% were VO3 stage females in March. In the sampled 2-year fish, the maximum levels were 50% spermiating males in February and 25% VO3 stage females in March. Control fish, which were exposed to the natural photoperiod (29°34′N), spawned during their natural season. The maximum levels for 1-year sampled control fish were 95% spermiating males and no females in December, while among 2-year sampled fish, maxima of 75% males in February and 45% VO4 stage females in November. Final average weights of photoperiod treated fish (1-year=430 g—regime 1, 400 g—regime 2; 2-year=582 g—regime 1, 518 g—regime 2) were significantly greater (p<0.05) than control fish (1-year=341 g; 2-year=476 g). Daily feed consumption (g/100 g fish) dropped from an average of 1.83 to 0.93 g for 1-year fish during August–December and from 0.88 to 0.54 g for 2-year fish during the same period. This was correlated with reduced autumn and winter water temperatures (26–20°C summer to winter change) and increased fish weight in all treatments. Daily feed consumption was also affected by the onset of spawning in the control and regime 2 (skeleton photoperiod) treatments of both 1- and 2-year fish. The efficiency of feed utilization (FCR) and protein and energy retention were all affected by the photoperiod regimes and followed the same pattern of decrease as weight gain, regime 1 (long day)>regime 2 (skeleton photoperiod)>control.     

Effects of photoperiod, stocking density and diet on growth in young spotted wolffish (Anarhichas minor olafsen)

Full scale experiments in tanks were conducted to elucidate the effect of photoperiod regime, dietary fat level and stocking density on growth in spotted wolffish. The study showed that continuous light (LD24:0) did not give a higher final mean weight or faster overall growth rate in spotted wolffish compared to constant 8 h light and 16 h darkness (LD8:16). However, there were indications that the fish needed time to adapt to a new photoperiod regime. The feeding experiment indicated a negative relation between dietary fat level and growth, where fish given 15% fat in the diet had a 13% higher final mean weight compared to fish on a diet with 20% fat. However, no conclusions could be made. The final mean weight was 10% higher at 25 kg/m² compared to 40 kg/m², indicating a negative impact of high stocking density on spotted wolffish.     

Dualistic feeding pattern of Nile tilapia (Oreochromis niloticus,L.) reared under different self‐feeding system conditions

Nile tilapia (Oreochromis niloticus) is one of the most important cultured species worldwide. The research aims to clarify the feeding characteristics, such as daily feeding pattern of Nile tilapia using a self‐feeding technique. The feeding pattern was conducted under two rearing conditions, indoor treatments under a controlled light regime (LD 12:12) and constant water temperature (25°C), and outdoor treatments under natural conditions which consisted of duplicate trials with two periods each. The outdoor treatment was carried out from early summer through late autumn in Mie, Central Japan. Daily self‐feeding activity of Nile tilapia in indoor treatments was nearly daytime feeding pattern, synchronizing with the given photoperiod (24 hr). However, the self‐feeding activity in the outdoor experiments from early summer to early autumn was almost daytime feeding pattern, but it became less clear and shifted to a nighttime feeding profile in late autumn. The results revealed that Nile tilapia has a dualistic capacity for demand‐feeding both in light and dark phases. These results might have been caused by the seasonal change in light intensity and/or water temperature. Information obtained from the self‐feeding experiments enables us to identify the influence of environmental changes on the physiological condition of farmed fish through their expression of appetite.     

Growth and feed performance,digestibility and acute stress response of juvenile grouper (Epinephelus fuscoguttatus) fed diets with hydrolysate from milkfish offal

Nutritional qualities of fish processing by‐products can further be improved through enzymatic hydrolysis. The objective of this study was to elucidate the efficacy of hydrolysed milkfish offal at different inclusion levels when fed to juvenile grouper, Epinephelus fuscoguttatus, with an initial body weight of 2.88 ± 0.06 g. The animals were fed for 56 days with seven diets supplemented with 0 (control), 5%, 15% and 25% of milkfish offal (MO) and milkfish offal hydrolysate (MOH). The diets were formulated to be isonitrogenous (45%) and isolipidic (11%). The diets were assigned to 21 tanks (15 fish per tank) with each diet having three replicates. Results from the experimental trials indicated that feed conversion efficiency, feed intake and weight gain of fish significantly (P < 0.05) improved when fed diets with MOH. No significant differences within the rest of the dietary treatments were observed. Survival rate (>90%) did not differ in all the dietary treatments. Proximate composition (crude protein, crude fat and ash) indicated no significant difference among fish fed from all the dietary treatments. Apparent digestibility of MOH indicated a 95% and 66% digestibility for protein and dry matter respectively. Plasma stress parameters (cortisol and glucose) were not influenced by the dietary treatment when fish were subjected to an acute stressor (5‐min chasing). Liver morphology indicated normal hepatocyte shape and the presence of lipid droplets in fish fed from all the dietary treatments. The results indicated that milkfish offal processed as hydrolysate can be utilized in grouper diets and can promote growth and feed efficiency when supplied at 10–15%.     

Observations and Techniques for Maturation, Spawning, and Larval Rearing of the Yellowtail Snapper Ocyurus chrysurus

Abstract.— This paper describes current techniques used at our laboratory for the controlled spawning, maturation and larval rearing of the yellowtail snapper. Juvenile yellowtail snapper were obtained from Florida and transferred to the Fisheries and Mariculture Laboratory in July 1990. Temperature and photoperiod manipulation resulted in precocial spawning in 1991, with sustained successive spawning beginning in February 1992. Average weekly spawning from 1992–1994 was 308,000 and 247,000 eggs/tank, with fertilization rates of 46.1 % and 32.5% for fish maintained in two separate spawning tanks. Observations on spawning activity from 1995 to 1996, during which a decreasing trend in egg and larval quality was observed, imply a possible problem with broodstock nutrition. Evaluation of feeding regimes during this period indicated a shift to a high (almost exclusively) usage of fresh squid and a reduction in fish and shrimp. Returning to a feeding regime of alternating feedings of fresh fish, squid. and shrimp have yielded improved spawning and egg quality. Larval rearing techniques using live and prepared feeds has resulted in an overall survival of 3% from egg to advanced juvenile. Growout of first generation (F1) juveniles yielded a marketable size (1 1b) fish in 25 mo. Spawning of F1 fish hegan in 1998. larval rearing and grow out of F2 fish are currently underway. Results demonstrate that yellowtail snapper culture is technically feasible; however. further research to develop species specific culture techniques will be required before the culture potential of this species can be accurately evaluated.     

Effects of starvation,subsequent feeding and photoperiod on flesh quality in farmed cod (Gadus morhua)

The study was designed to investigate the effect of four cycles of 5 weeks starvation followed by 10‐week refeeding compared with daily feeding under either natural photoperiod or continuous light (LL) regime on body composition and flesh quality in Atlantic cod in sea cages, northern Norway. The fish were sampled for body composition and flesh quality parameters at the start of the trial, twice at the end of a 10‐week feeding period and twice at the end of a 5‐week starvation period. There was effect of both feeding and light regime on growth, the two starving groups losing weight during starvation and regaining weight during refeeding, and the group under LL being heavier. But, the mean overall growth did not vary between groups. Starvation/refeeding regime resulted in higher slaughter yield, but no overall effect was seen on hepatosomatic index, water content, water holding capacity (WHC), muscle pH, hardness or flesh colour compared with control groups. Continuous light increased gutted weight and slaughter yield, lowered WHC and depressed maturation compared with fish under natural light regime. Increased growth rate resulted in softer fillets and lower muscle pH.     

The relation between age at first maturity and growth in Atlantic halibut (Hippoglossus hippoglossus) reared at four different light regimes

The effect of extended photoperiods on growth and age at first maturity was investigated in 166 (79 females and 87 males) individually tagged Atlantic halibut. The halibut were reared at 11°C on four different light regimes from 10 February to 6 July 1996: simulated natural photoperiod, (LDN), continuous light (LD24:0), constant 8 h light and 16 h darkness (LD8:16) and LD8:16 switched to continuous light on 4 May 1996 (LD8:16–24:0). From 6 July 1996 to 9 February 1998 the LD24:0 and LD8:16–24:0 were reared together under continuous light and the LDN and LD8:16 together under natural photoperiod. Juveniles subjected to continuous light exhibited faster growth than those experiencing a natural photoperiod or a constant short day. Moreover, the results suggest an overall growth enhancing effect of continuous light in females, but not in males. No females matured during the trial, but the proportion of mature males differed between the photoperiod groups, with significantly fewer males maturing in groups reared at continuous light. Independent of photoperiod regime and maturation status, females were significantly bigger than males from 14 April 1997 onwards. Immature males were bigger than maturing males from 23 March 1996 onwards. As continuous light reduced maturation at age 2+ in males, this could be used to reduce precocious maturation in males.     

Influence of feeding regime on intraspecific competition, fin damage and growth in 1+ Atlantic salmon parr (Salmo salar L.) held in freshwater production cages

The feeding behaviour, growth and feed conversion ratio (FCR) of cage‐held Atlantic salmon parr (Salmo salar L.) were studied when in 576 m³ (12 m × 12 m × 4 m) commercial freshwater cages under ambient water temperature (8.84±3.53°C) and photoperiod (11.02±2.05 h) for 205 days. The effect of feeding regime on fin damage was also investigated. Six groups (n=31 234±2051 fish group⁻¹, initial stocking density 1.25±0.14 kg m⁻³) were fed to satiation using either (a) an imposed regime involving scheduled, fixed ration feeding every 10 min from dawn till dusk or (b) on demand from dawn till dusk using commercial interactive feedback systems. During feeding, there were no significant differences in aggression although swimming speeds and turning angles were significantly higher in fish under the imposed regime. On‐demand feeding significantly reduced the incidence of dorsal fin damage. There was no clear relationship between fish size, feed regime and the incidence of fin damage until 1 week before the fish were transferred to marine cages, when the smallest fish under each feeding regime had the highest incidence of fin damage. Interestingly, growth did not differ between regimes, but fish under the imposed regime were significantly overfed and achieved higher FCRs.     

Environmental Manipulation of Growth and Sexual Maturation in Yellow Perch, Perca flavescens

Yellow perch, Perca flavescens, exhibit sexually dimorphic growth detected as the fish enter puberty. The purpose of this study was to evaluate the differential influences of photoperiod and temperature on the sexual maturation and dimorphic growth pattern of yellow perch. Four combinations of constant (CP) or natural (NP) photoperiod with constant (CT) or natural (NT) temperature were evaluated (CPCT, CPNT, NPCT, NPNT). Following 6 months of growth, results indicate that (1) CT is the strongest promoter of overall growth regardless of photoperiod. Perch reared under CT were 26.4 ± 8.1 g heavier than perch reared under NT (P < 0.0001). (2) CP also promotes overall growth regardless of temperature. CP perch outgrew NP perch by 7.0 ± 8.1 g (P < 0.0872). (3) NP (decreasing) initiates maturation in yellow perch regardless of temperature. (4) NT is required for late maturational processes. While both NP groups initiated maturation, only NPNT females were able to recruit oocytes to a vitellogenic stage. Only NPNT males were able to sustain spermiation to the end of the study. (5) CPCT confer the best overall growth performance, fully inhibit maturation in both genders, and suppress a sexually dimorphic growth pattern up to 53 g average weight. These results indicate that using a CPCT regime during intensive fingerling production will produce a larger, more uniform fish population that could alleviate losses as a result of cannibalism. Perch that remained immature did not exhibit a dimorphic growth pattern.     

Progress in Controlled Maturation and Spawning of Summer Flounder Paralichthys dentatus Broodstock

Abstract— Wild-caught, adult summer flounder Paralichthys dentatus (avg. wt. = 740 g; range = 264–1,540 g; N = 60), collected in northeastern US coastal waters during October 1994, were transported to Vero Beach, Florida in March 1995 and held in 2.6-m³ indoor tanks through November 1995 under two artificial photothermal regimes: (1) natural regime, simulating natural habitat conditions; and (2) accelerated thermal regime, with seasonal temperature changes advanced by one month. A third group of fish was held in outdoor tanks under ambient photothermal conditions. Under all photothermal conditions, onset of vitellogenesis was associated with declining daylength and temperature, beginning in the accelerated group, then progressing to the natural and the ambient groups. From 20 September to 28 November 1995, 23 vitellogenic stage females from the accelerated and natural regimes were implanted with a cholesterol-cellulose pellet containing LHRH-a (100 μg/kg body wt). Females with initial mean oocyte diameters ranging from 258–456 μm spawned voluntarily 2.5–5.5 d postimplantation, while no maturational response was obtained from females with mean diameters ranging from 165–231 μm. Two females were spawned twice during the study period by LHRH-a pellet implantation. Infrequent, natural spawning without hormone intervention was also obtained. Females released from 22.7–396.9 × 10³ eggs on the first day of spawning, with fertilization and hatching rates of 0–93.470 and 0–81.1%, respectively.     

Economics of milkfish (Chanos chanos) production in Hawaii*

Abstract

Economic evaluations of commercial milkfish (Chanos chanos) growout systems were made based on current Hawaiian fishpond, pond and tank culture techniques in Hawaii. Based on the observed practices of milkfish culture as a secondary or tertiary crop, capital costs and several operating costs were pro‐rated to accurately depict current farm practices. For a target harvest weight of 0.80 lb, the study estimates the total production cost for milkfish production at $3.31/lb for the pond system, $3.81/lb for the tank system and $1.84/lb for the Hawaiian fishpond system. At a sale price of $3.00/lb and seed cost of $0.25/fingerling, only the Hawaiian fishpond system is profitable under a 20‐year project life. When considering variable costs alone, the production cost is $1.78/lb for the pond system, $2.33/lb for the tank system and $1.53 for the Hawaiian fishpond system, yielding returns on variable costs of 67%, 30% and 59% respectively. Analyses of profit sensitivity to sale price, production yield, labor, feed and stocking indicate that sale price, as expected, has the largest impact on profitability, followed by feed. The results of this study are consistent with the Hawaii farmers’ view of milkfish as a secondary specie to core production based upon current market conditions and input requirements.     

The effect of timing of extended photoperiod on growth and maturity of brook trout (Salvelinus fontinalis)

The influence of timing of extended photoperiods on growth and maturity of brook trout was investigated in a 112‐day experiment. The fish with mean initial weight of ~192 g were reared under four light regimes: one control group with natural ambient photoperiod and three groups exposed to an 18L:6D regime initiated at days 1, 23 or 46 of the growth trial. Light‐emitting diodes, with intensity of 250–1000 lux, depending on the distance from the light source, were used for extending light periods. There was a positive effect of prolonged day length on fish growth (p < 0.05), and a delay in gonad development and sexual maturity. Significantly higher numbers of sexually mature fish were found among controls groups, regardless of sex. Survival rate was not affected by light regime. This study demonstrated that the short‐term expansion of the photo period delayed maturation and increased the growth rate of brook trout.     

Artificial Propagation of Mutton Snapper Lutjanus analis, A New Candidate Marine Fish Species for Aquaculture

Abstract Wild-caught mutton snapper Lutjanus analis , a high-value marine food fish species, matured in flow-through seawater (36 g/L) tanks after 3 yr in captivity. On 31 May 1995, a female with a mean oocyte diameter of 382 μm was injected with human chorionic gonadotropin (HCG) (500 IU/kg body wt.) followed 24 h later by a second injection (1,000 IU/kg body wt.). At the time of the second injection, three males were injected with HCG (500 IU/ kg body wt.). Voluntary spawning occurred 33 h after the first injection, with a total of 534, 781 eggs released. Fertilization rate was 75.7%, while average diameter of fertilized eggs was 783 μm. Embryos were stocked in a 30-m³ outdoor tank at a density of 10.5/L. On day 2 post-hatching (d2ph), larval density was 8.61 larvae/L, and average notochord length was 2.6 mm. Larvae were fed ss-type rotifers from dl-d28ph, Artemia nauplii from 0–08ph, and artificial diets (52–48% protein) from d24-d38ph. On d38ph, fish averaged 0.308 g and 22.2 mm standard length. Survival (from d2ph) was 14.3%, with a total of 36,900 post-metamorphic juveniles produced. On d97ph, 1,390 hatchery-reared juveniles (avg. wt. = 10.5 g) were stocked into two 14.5-m³ recirculating seawater tanks (695 fish/tank; 48 fish/m³) and fed a 56% protein pellet. After 168 d, fish averaged 140.8 g, with a survival rate of 97.8% and a feed conversion ratio (dry wt./wet wt.) of 1.2. These preliminary results reveal the mutton snapper to be a prime, new candidate species for commercial cultivation.     

Effects of constant light on haematological parameters of cultured rainbow trout (Oncorhynchus mykiss) in the Southern Hemisphere

The effects of artificial photoperiod regimes on reproductive patterns have been studied in several species, as have haematological parameters. However, information on how artificial photoperiods may affect blood components is scarce, especially under field conditions. We have assessed the effects of constant light [long day (LD) photoperiod: 24 h (light):0 h (dark)] on haematological parameters of cultured rainbow trout in Chile (Southern Hemisphere). In the initial stage (March up to June), two groups of fish were maintained under similar conditions and under the ambient (natural) photoperiod (NP). One group was then placed under the LD photoperiod regime for 2 months (June/July), following which it was returned to␣the NP (August–January); the control group remained under the NP throughout the experiment (March–January). All fish were assessed for haematological parameters and growth performance at various times during the experiment. During the initial stage, no differences were found between groups. However, at the end of the LD 24:0 period, the LD fish had increased haematocrit values and erythrocyte numbers and diminished mean corpuscular haemoglobin. After the LD fish had been returned to the NP, they developed secondary sexual characteristics and had a 40–44% decrease in the number of leukocytes.     

Effects of photoperiod on growth and spawning efficiency of Nile tilapia (Oreochromis niloticus L.) broodstock in a recycling system

This study was conducted to evaluate the effects of photoperiod on the growth, feed conversion ratio (FCR) and spawning performance of Nile tilapia (Oreochromis niloticus) broodstock. Duplicate groups of two males (66±3.04 g) and six females (50.5±1.58 g) were stocked in 0.4 m³ fibreglass tanks in a recirculating water system at a male:female ratio of 1:3. The fish were subjected to four photoperiod treatments: 24:0 light:dark (L:D), 18L:6D, 12L:12D and 6L:18D. Light intensity was kept constant at about 2500 lx throughout the study. The fish were fed a commercial tilapia diet (35% crude protein and 16.6 MJ GE kg⁻¹) at a daily rate of 2–3% of tank biomass, twice a day, for 130 days. Males grew significantly faster than females under all photoperiod regimes. The best growth rate and FCR were attained at 18L:6D, followed by 24L:0D, 12L:12D and 6L:18D respectively. The number of eggs per female, number of eggs per spawn and number of spawnings per female were all significantly higher in the 12L:12D treatment than in all other photoperiod cycles. Interspawning intervals and days elapsed per spawn were also shorter in the 12L:12D treatment. The time to first spawning was slightly longer in the 24L:0D and 6L:18D than in 12L:12D and 18L:6D light phases. The 18L:6D and 6L:18D photoperiods produced the lowest spawning performance. It is concluded that a 12L:12D photoperiod regime should be adopted for maximum fecundity, seed production and spawning frequencies of Nile tilapia broodstock reared in intensive, recirculating systems. If maximum reproduction is desired, a near‐natural day length photoperiod should be used.     

Breeding-related growth of captive Sparus aurata (Teleostei,Perciformes)

Growth is arrested in male and female Sparus aurata during gonadal recrudescence and spawning. Growth and feeding rates of fish exposed to a constant long photoperiod ($\text{16L}\text{8D}$) were significantly higher than those of fish under a natural photoperiod. When the experimental photoperiod was shortened, fish underwent gonadal recrudescence and reduced feeding, and their growth was arrested. Fish under the long photoperiod regime reached the commercial weight of 350 g six months earlier than the controls.     

Growth and salt-water tolerance of juvenile Atlantic salmon, Salmo salar, reared under different combinations of dietary carbohydrate and photoperiod regime

The present study evaluated how different photoperiods, carbohydrate sources and inclusion levels influenced growth, plasma, organ and body compositions in Atlantic salmon (Salmo salar). Four different diets were used, containing 10 or 20% starch on a dry matter basis, using gelatinized corn (C10 and C20) or wheat (W10 and W20). Two different photoperiods were used, Continuous (Con) light throughout the study, Winter (Wi) two initial weeks of continuous light, thereafter 6 weeks of short day, ending with 6 weeks of continuous light. The winter regime resulted in reduced growth rate compared with continuous light. All Wi groups were smaller than Con groups when the experiment was terminated, except for fish given diet C10. Diet W10 resulted in better growth compared with all other groups when exposed to Con. regime. Atlantic salmon fed with diets containing 20% starch had lower growth rates than fish fed diets containing 10% starch, when the same starch source and light regime were compared. All fish belonging to the Con group exhibited similar and higher condition factors compared with fish from groups Wi. Condition factor was not influenced by dietary starch source. Higher whole body lipid concentrations were found when fish were given the corn compared with the wheat diets, without any responses to starch level or light regime. Whole body protein showed increased values in fish exposed to regime Wi compared with Con, without any influence from dietary manipulation. Liver glycogen values and hepatosomatic index reflected dietary starch levels and were significantly influenced by light regime, whilst muscle glycogen levels varied only as a response to light regime with lower values in fish from the Wi compared with the Con groups. Light regime influenced plasma glucose levels, except in groups fed with diet W10. All measured plasma nutrient concentrations were within normal ranges. At the end of the feeding period, all fish were evaluated for glucose and salt water tolerance to ascertain whether diet and/or light regime influenced glucose regulation capacity and/or smolt quality. Fish fed with 20% starch had reduced osmoregulatory ability measured as plasma chloride after a seawater challenge test. Fish from the Wi regime, but not from the Con regime developed characteristics associated with smoltification. Glucose tolerance in Atlantic salmon was substantially influenced by both photoperiod regime and diet. Fish reared under the Wi photoperiod showed reduced glucose regulation capacity compared with fish held under continuous light. Glucose regulation capacity was also reduced in fish adapted to the highest starch levels.     

Survival of captive milkfish Chanos chanos Forsskal broodstock subjected to handling and transport

The survival of milkfish broodstock (body weight range 1–11 kg) was determined until 30 days after handling and transport in open tanks or in sealed oxygenated bags containing chilled sea water (20–25 °C). Maintenance of cool sea water was achieved by the gradual addition of ice chunks or frozen gel packs. A survival rate of 50% after transporting fish at a loading density of 45 kg m^?3 for 4 h in open tanks was not significantly different from those that were handled but not transported (86%). Similarly, survival rates (67–83%) among broodstock confined for 8 h in chilled sea water at 40 and 60 kg m^?3 were not significantly different from each other or from a group not subjected to confinement. Nevertheless, low dissolved oxygen (DO) and accumulation of total ammonia–nitrogen beginning 1 h after transport and confinement may be responsible for low survival rates of milkfish in open tanks. In contrast, all milkfish survived 10 h of overland transport in sealed bags with chilled and diluted (28 g L^?1) sea water. Likewise, all milkfish survived after being bagged and immediately transferred to a communal rearing tank, or bagged and placed in a styrofoam box for 10 h. Except for total ammonia–nitrogen levels, which increased slightly (0.7–0.8 mg L^?1) above background, seawater temperature (20–24 °C), salinity (28 g L^?1) and DO (6 to > 20 mg mL^?1) titres in transport bags were maintained during the 10‐h test. The effectiveness of handling and transporting milkfish broodstock in sealed bags containing chilled sea water was verified in actual field trials. Spawning of sexually mature milkfish subjected to these stressors was not impaired. These results demonstrate that mortalities of large milkfish broodstock can be minimized when fish are handled and transported in sealed oxygenated bags containing chilled sea water.