Modeling larval Calanus finmarchicus on Georges Bank: time-varying mortality rates and a cannibalism hypothesis

Throughout the North Atlantic, the copepod Calanus finmarchicus dominates the zooplankton biomass, linking primary production and higher trophic levels. On Georges Bank, the peak abundance of larval (naupliar) stages occurs in March–April and represents a potential source of prey for cod and haddock larvae. Following this maximum, naupliar abundance declines dramatically, reaching a minimum in May and increasing again in June. Explaining the naupliar seasonal cycle is critical for predicting climate effects on C. finmarchicus dynamics, including whether environmental variability may lead to a mismatch with larval fish. Here, an age-within-stage population dynamics model is used to investigate the factors controlling the temporal variation of C. finmarchicus nauplii in three Georges Bank sub-regions. The model incorporates temperature- and food-dependent development and egg production, as well as female abundance derived from the US Global Ocean Ecosystem Dynamics (GLOBEC) program. Use of field-estimated constant mortality rates overestimates May abundances by as much as an order of magnitude. These data/model discrepancies can not be explained by temperature or food-limitation effects on physiological rates. Instead, accurate simulation requires use of time-varying early stage mortalities, which differ from published estimates in both magnitude and trend. These mortality rates are correlated with C. finmarchicus female abundance, implying cannibalism as a possible regulatory factor. Thus, the biological control of predation (including cannibalism) must be considered to predict the effects of climate on C. finmarchicus and associated larval fish populations.     

Use of a discontinuous Percoll gradient technique for the separation of channel catfish, Ictalurus punctatus (Rafinesque), peripheral blood leucocytes

Abstract The use of a discontinuous density Percoll gradient in the separation of channel catfish peripheral blood leucocytes is described. The procedure yielded fractions enriched in monocytes and lymphocytes at the 1·060–1·065 g/ml interface, lymphocytes at the 1·065–1·070 g/ml interface, and neutrophils at the 1·070–1·080 g/ml interface. Cell purities among fractions ranged from 14·4–51·6% for monocytes, 61·4–72·8% for lymphocytes, and 60·4–79·2% for neutrophils. Factors influencing the outcome of the separation procedure include the use of pooled blood samples and calcium- magnesium-free salt solutions.     

Annual changes in distribution depths of bighand thornyhead <Emphasis Type="Italic">Sebastolobus macrochir</Emphasis> off the Pacific coast of northern Honshu,Japan

ABSTRACT:   Body size dependent distribution patterns of bighand thornyhead Sebastolobus macrochir were examined using bottom trawl surveys in the Tohoku area, off the Pacific coast of northern Honshu, Japan. In northern and southern Tohoku, distribution depths of ≤10-cm standard length (SL) fish increased from 500–600 m in 2003 to 600–700 m in 2005 with an increase in density of 11–20-cm SL fish at depths of 500–600 m. In 2004–2005, small fish (≤10 cm SL) were distributed in deeper waters than large fish (11–20 cm SL). In ≤20-cm SL fish, the main distribution depths changed from 300–600 m in 1997–2002 to 500–600 m in 2003 in southern Tohoku, but not in northern Tohoku. Stepwise multiple regression analysis showed that negative correlations were found in biomass densities between a few demersal fish species and bighand thornyhead at depths of 300–400 and 400–500 m in southern Tohoku. These results suggest that distribution of bighand thornyhead was affected by intra- and interspecific competitions in the Tohoku area.     

Masculinization of fighting fish, Betta splendens Regan, using synthetic or natural androgens

Abstract. The effects of two synthetic androgens, 17α-methyltestosterone (5–50mg/kg food), 19-nor-ethynyltestosterone (2–50 mg/kg food) and two natural androgens, 11 ketotestosterone (10–60mg/kg food) and androstenedione (20–100mg/kg food) were investigated in the fighting fish, Betta splendens Regan. Androgens were administered for 40 days from the first day of feeding. Masculinization occurred in 100% of individuals fed 8, 15, 60, 90 mg/kg food 19–nor–ET, 17α–MT, 11–KT and AT respectively. Mortality due to treatment of natural steroids was significantly less than that with the synthetic steroids. Sex–reversed males were sexually functional and their genotype was identified by progeny testing. Sex-reversed males produced 100% female monosex when mated with normal females, indicating that the mechanism of sex determination in this fish is homogametic female and heterogametic male.     

Strategies for Development of Rotifers as Larval Fish Food in Ponds

Strategies to sustain rotifer peak biomass, distribution of rotifer resting eggs in the sediment, and relationship between rotifers and larval fish growth were studied in a series of pond experiments. After the ponds were filled with water, herbivorous rotifers (e.g., Brachionus calyciflorus ) developed first, but were gradually replaced by predatory rotifers (e.g., Asplanchna ). Subsequently, herbivorous cladocerans (e.g., Moina sp) eventually replaced rotifers and dominated the zooplankton community. The occurrence of Asplanchna and Moina indicated the decline of B. calyciflorus . Peak rotifer biomass developed 8–10 d after the ponds were filled with water at 20–25 C, 10–15 d at 17–20 C, 15–20 d at 15–17 C, 20–30 d at 10–15 C, and >30 d at < 10 C. The abundance of resting eggs in the top 5-cm sediment varied from 6 to 83/cm². About 25% of resting eggs were buried in the top 5-cm sediment but the number of resting eggs decreased with increased sediment depth. Optimum rotifer biomass for silver carp Hypophthalmichthys molitrix larvae stocked at 1,500,000/ha was 20–40 m/gL. High rotifer biomass (>20 mg/L) usually lasted 3–5 d, but could be prolonged by pond fertilization or cladoceran controls. A weekly application of dipterex at 0.05 mg/L reduced cladoceran biomass but enhanced rotifer biomass. Our results indicate with a careful management plan it is possible to synchronize the rotifer development with larval fish stocking.     

Chemical Budgets for Organically Fertilized Fish Ponds in the Dry Tropics

Chemical budgets were determined for nitrogen, phosphorns, dissolved oxygen and chemical oxygen demand for three 0.1-ha earthen ponds stocked with Onwchrornis nilotieus at the El Carao National Fish Culture Research Center, Comayagna, Honduras, for two 150-d culture periods, corresponding to the rainy and dry seasons. Layer chicken litter was added to ponds weekly at 500 kg dry matter/ha. Concentrations of nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) in pond water increased during each season. No significant seasonal differencea in concentrations of water quality variables were observed. Chicken litter added to ponds represented 92–94% of N input, 93–95% of P input, and 43–52% of COD input. Photosynthesis by phytoplnnkton provided 47–56% of COD and 98% of dissolved oxygen (DO) added to ponds. Net inward diffnsion of oxygen added 1.2–1.5% of total DO. Regulated inflow was a minor source of nutrients, and contributed 3–4% of input N, 3–4% of input P, 1% of COD input, and 1% of DO input. Nutrient inputs from rain were ≤1% of total for each nutrient. Fish harvest accounted for 18–21% of total N, 16–18% of total P and 2% of COD added to ponds. Community respiration accounted for 48–57% of COD and 99.5% of DO added to ponds. Nutrient losses in pond effluent at draining were: 7–9% of total N, 29–37% of total P and 2–3% of COD. While measured gains exceeded measrued losses, significpntly greater N, P and organic matter concentrations in pre-drain samples indicated pond mud was a major sink for added nutrients, accumulation in mud represented 70% of total N, 35–40% of total P, and 38–46% of COD.     

Growth and ontogenetic migration of greeneye Chlorophthalmus albatrossis in Tosa Bay, Pacific Coast of South-Western Japan

ABSTRACT:   Growth and ontogenetic migration of greeneye Chlorophthalmus albatrossis were studied in the area from 100–400 m depths in Tosa Bay, from April 1996 to March 1997, using samples collected by an otter trawl net with a 1.3 mm mesh cod end. In the monthly changes of the standard length (SL) composition, four year classes were recognized, although the third- and fourth-year classes were not clearly separated in all the monthly samples. Individuals of 40–50 mm SL settled on the bottom of the 150–200 m depth zone from August to February. By May and June, they grew to 75–80 mm SL modal size, and migrated to 200–300 m depth. In one year after settlement, they grew to 125–130 mm SL, and migrated to 300–350 m depth. They grew to a maximum of 160 mm SL and were not sampled in the winter three years after settlement, suggesting either migration or mortality. Seasonal changes in the gonadosomatic index for combined samples of males and females showed that greeneye did not mature in Tosa Bay. It is suggested that the planktonic larvae are transported from the spawning grounds, the location of which remains unknown.     

Effect of synthetic GnRH analogues and dopamine antagonists on the maturation of Pacific mullet, Mugil so-iuy Bas.

Abstract. The effect of two GnRH-As – des Gly¹⁰ (D-Ala)⁶ LHRH and des Gly¹⁰ (D-Tle)⁶ GnRH in total doses 10–249mu;g/kg – and four neuroleptics – pimozide, sulpiride, metoclopramide and isofloxythepin in total doses 1–50mg/kg - and environmental temperatures on the development of final stages of Pacific mullet oogenesis was investigated. The best technique of those used by us for spawning stimulation of Pacific mullet, Mugil so-iuy Bas., females is shown to be administration of neuroleptics in doses of l-8mg/kg with posterior injections on GnRH-A in doses of 25 and 50mu; g/kg applied 4 and 28h respectively after the neuroleptic injection. At water temperatures below 17°C, ovulation does not occur unless the optimal stimulation is applied.     

Growth of the fourspine sculpin <Emphasis Type="Italic">Cottus kazika</Emphasis> in the Gonokawa River,Japan, and effects of water temperature on growth

ABSTRACT:   The fourspine sculpin Cottus kazika is indigenous to Japan and found in Honshu except for the waters facing the Seto Inland Sea, and was also found in southern Shikoku and eastern Kyushu. This species has a catadromous lifestyle and migrates as juveniles from the sea to the middle reaches of rivers to grow. The growth pattern of this fish was investigated by a mark-and-recapture method from July 1994 to December 1996, in the Nigorikawa River, a tributary of the Gonokawa River system, Shimane Prefecture. 0-year-old fish of 50–70 mm total length ( TL ) occurred in the study area from June to July, grew to 90–140 mm  TL by the following April, and attained 160–210 mm  TL by December. This fish grew rapidly in September–November and April–July, almost ceasing to grow in July–September. It seems that this stagnant growth phase in summer is a characteristic of the seasonal growth pattern of C. kazika . A rearing experiment indicated that the growth rate of C. kazika was higher at 16–22°C than at 12–14 and 24–26°C. This result supports the field evidence of a stagnant growth phase in summer in the Nigorikawa River.     

Fatty acid and lipid content of Oreochromis niloticus L. in Ethiopian lakes — dietary effects of phytoplankton

Abstract— Herbivorous tilapia fish, Oreochrornis niloticus L. (Cichlidae), collected from five Ethiopian lakes were analyzed for lipid and fatty acid contents of the dorsal muscle using spectrophotometry and gas-liquid chromatography. The results showed remarkable variation between the lakes in both the lipid and total fatty acid content of the fish, 1.7–21 and 1.6–9.3% of dry weight (DW), respectively. Most fish from Lakes Haiq and Chamo contained higher levels of fat (≥ 10% DW) compared to fish from Lakes Ziway, Langeno and Awassa which contained ≤ 5% DW fat. A total of 28 fatty acids were identified. The saturated fatty acids ranged from 5.3–30 mg. gg⁻¹ DW, monounsaturated Fatty acids from 1.3–30 and polyunsaturated fatty acids from 6.8–29 mg. g⁻¹ DW. The most abundant fatty acids were palmitic acid, docosahexaenoic acid (DHA), oleic acid, stearic acid, palmitoleic acid, arachidonic acid and eicosapentaenoic acid (EPA). EPA and DHA alone amounted to 2.6–15 mg. g⁻¹ DW. The ω3/ω6 ratios ranged from 1.3–7.6 and L. Haiq fish showed the highest ratios, 5.1–7.6, indicating that the fat was of high nutritional quality. The reason for such variation is probably the varied diet available to the fish in the various lakes, This study, along with previous reports, confirms that the phytoplankton flora constituting the diet of O. niloticus varies greatly between the study lakes. The variation in phytoplankton is also reflected by the fatty acid pattern of net samples taken from the study lakes.     

Spawning by Captive Serranid Fishes: A Review

The current available information on spawning by serranid fishes in captivity is reviewed. Much work has been done on members of the family Serranidae because of their value as food or ornamental fish. At least 31 species have been induced to ovulate with hormones, and at least 23 species have spawned voluntarily (without chemical treatment) in captivity. Typically, a serranid female with fully-yolked oocytes will ovulate within 24–72h (usually 36–50h) after the first of 1–3 injections of 500–1,000 IU human chorionic gonadotropin/kg body weight. Similar results have been obtained for several species given 1–3 injections of 10–50μg luteinizing hormone-releasing hormone analog/kg body weight. Voluntary spawning has occurred mostly with well-fed uncrowded fish during the natural spawning season under conditions of ambient temperature and partial or total natural light. The necessary temperature range for spawning varies among species, and daylength seems to be a less important stimulus than temperature for serranids.     

Essential fatty acid requirements of larval gilthead sea bream, Sparus aurata (L.)

Abstract. Two experiments were carried out to study the effect of n -3 HUFA levels in rotifers on survival, growth, activity and fatty acid composition of gilthead bream, Sparus aurata (L.), larvae. From the third to the 15th day after hatching, gilthead bream larvae received one of the three kinds of rotifers containing different percentages of n –3 HUFA. Moisture, crude lipid, saponifiable matter and fatty acid composition of total lipids of rotifers and larvae were determined.
A good correlation was found between larval growth and n –3 HUFA levels in rotifers. Larval survival was also significantly improved by the elevation of the n –3 HUFA levels in rotifers. A high occurrence of hydrops was registered in larvae fed with EFA-deficient rotifers. The n –3 HUFA levels in the larvae were increased by the elevation of n –3 HUFA contents in rotifers. However, n –9 fatty acids in the larvae remained almost constant, regardless of the different 18:1 n –9 contents in rotifers. Therefore, the ratio of oleic acid to n –3 HUFA, known to be an indicator of the EFA deficiency in fish, was reduced by the elevation of the n –3 HUFA levels in rotifers.     

Common pearl oysters in China, Japan, and Australia are conspecific: evidence from ITS sequences and AFLP

ABSTRACT:   To elucidate the species status of Pinctada fucata in China, P. fucata martensii in Japan and P. imbricata in Australia, one population of each taxon was studied using internal transcribed spacer 1 and 2 (ITS1, and ITS2) and amplified fragment length polymorphism (AFLP) markers. ITS1 and ITS2 were 401–405 and 229–237 bp long, respectively. Twenty-nine ITS1 and 15 ITS2 unique genotypes were obtained from 44 and 34 individuals, respectively, with some genotypes shared by two or three populations. In AFLP analysis, each individual exhibited a distinct phenotype. No population had diagnostic markers. Mean genetic divergences within and among the three populations were very low and overlapped (between-population: 0.7–0.9% for ITS1, 0.9–1.3% for ITS2, and 53.3–55.6% for AFLP; within-population: 0.5–0.9% for ITS1, 0.8–1.2% for ITS2, and 50.4–53.6% for AFLP). Low levels of genetic differentiation were observed among the three populations while the Australian population is partially genetically isolated. Under an infinite allele model, genetic differentiation among populations was not significant based on a permutation test. Under an infinite site model, most F _ST values were not significant for ITS data although they were significant for AFLP data. Network analysis using ITS data indicated that individuals from the same population did not cluster together. Analysis of molecular variance ( amova ) demonstrated that > 94% variation was contributed by within-population variation. These findings suggest that the three taxa are conspecific and Pinctada fucata is the correct name.     

Radula development in abalone Haliotis discus hannai from larva to adult in relation to feeding transitions

ABSTRACT: The radula morphology of Haliotis discus hannai was examined by scanning electron microscope from the larval to the adult stage. The radula of competent larvae contained 11–13 transverse rows of teeth after 6–7 days at 20°C. The number of rows increased to 25–30 during the first several days after settlement, but then remained approximately constant throughout the post-larval period, increasing again in abalone larger than 4 mm in shell length (SL). In post-larvae < ~1 mm SL, only two pairs of lateral teeth (L1, L2) were present in the larval radula. An additional three pairs of lateral teeth (L3–L5) were added progressively as post-larvae grew from 0.9 mm to 1.9 mm SL. Marginal teeth were added steadily from one pair in larvae to 30–40 pairs at 3–4 mm SL, 70–80 pairs in 30–40 mm juveniles, and 70–90 pairs in 90–100 mm adults. The serrations on the working edges of the rachidian (R) and lateral teeth became less pronounced as the abalone grew. Nearly all serrations disappeared from the rachidian (R) and inner lateral teeth (L1, L2) by ~2 mm SL, and from the outer lateral teeth (L3–L5) by 20 mm SL. For abalone larger than 1.5 mm SL, the L3–L5 teeth became longer and more pointed, which increased the space between adjacent rows of teeth. Post-larvae < 1 mm SL had highly curved teeth with clearance angles of approximately or less than zero, whereas larger abalone had positive clearance angles. These radula developments appear to be related to transitions in feeding habits from microbial to macroalgal diets.     

Variability of community structure of Copepoda related to El Niño 1982–83 and 1987–88 along the west coast of Baja California Peninsula, Mexico

Copepod community structure and abundance of the most abundant species were studied during 15 cruises made between 1982 and 1989 along the west coast of the Baja California Peninsula, Mexico. The number of species and species diversity (Shannon's index) for each sampling station of the oceanographic cruises were obtained. Though the zone was dominated during the year by the tropical copepod component, similarities between El Niño 1982–83 and 1987–88 were observed. Tropical-equatorial populations were added to the regular tropical composition (50%) of the community of copepods resulting in a wide distribution of those populations in 1982–83 and in 1987–88. The scenario in 1984–89 (without 1987–88) was significantly different from both El Niños because of the sea surface temperature, the species diversity, and the tropical copepod component, although 1982 was similar to 1985 in diversity index and number of species. Environmental conditions prevailing along the west coast of Baja California during El Niño indicate that in 1982–83 the effect on the copepod community was greater than during the 1987–88 event.     

Mass Production of Striped Patao Eugerres brasilianus Juveniles in Cuba

Abstract.— Two spawning and larval rearing trials with striped patao Eugerres brasilianus were conducted at Tunas de Zaza, Cuba, to develop a method for experimental-scale mass production of juvenile fish. Mature striped patao were captured from coastal lagoons in September 1988 and January 1989. Sexually mature females and males were induced to spawn by treatment with human chorionic gonadotropin (HCG). After spawning, eggs were collected and placed in 1.2-m³ cylindroconical fiberglass incubators at densities of 150 and 200 eggs/L. About 1 h before hatching, eggs were transferred to 5–m³ concrete tanks. Larvae were fed a mixture of marine microalgae, rotifers, copepods, and Artemia nauplii; artificial food was supplied at 30 d post-hatch as a shrimp diet with 25% protein and 0.1–0.4 mm particles. Fourteen of 20 females spawned after 2 or 3 HCG injections (total dose = 6–10 IU/g body weight). Fecundity was 467–2,167 eggs/g body weight. Egg incubation time in seawater (38–39 ppt salinity) was 15–17 h at 29–30 C and 21–23 h at 25–26 C, with 98–100% hatching rate. The oil droplet and yolk sac were consumed by 3 to 5 d post-hatch and first food (rotifers) was eaten during second day. High larval mortalities began after the first month. Growth in 39- ppt seawater was faster (0.41 ± 0.01 md/d) at 29.1 ± 0.3 C than at 25.2 ± 0.2 C (0.27 ± 0.008 mm/d). Overall survival was 6–12.5% with tinal densities of 5–10 juveniles/L after 48–60 d. A total of 132,000 juveniles was harvested from the two rearing cycles.     

Unicauda magna sp.n. (Protozoa: Myxozoa): a new myxozoan from the fin tissues of the fathead minnow, Pimephales promelas Rafinesque

Abstract. Unicauda magna sp.n. (Protozoa: Myxozoa) was found in hatchery-raised fathead minnows, Pimephales promelas (Cyprinidae) from Pennsylvania. A large number of whitish-coloured cysts were located in the tissues of the pectoral, pelvic and caudal fins of infected fish. Spore dimensions (in μm) based on 30 measurements (10 spores/cyst) included the following: total length, 109.6 (75–170); spore body length, 15.5 (14–17); spore body thickness, 12.1 (10–13); spore body width, 13.2 (12–14.5); tail length, 94.1 (60–154); polar capsule lengths, 8.6 (7.5–9.5); polar capsule width 4.1 (3.0–5.0); sutural ridge width, about 1. The tail and body of the spores differed in colour when stained with each of three dyes. They are, therefore, composed of different material.     

Age and growth of the silky shark Carcharhinus falciformis from the Pacific Ocean

ABSTRACT:   The present study estimated the age and growth of the silky shark Carcharhinus falciformis in the Pacific Ocean. Samples and biological data were collected from Japanese tuna longline and purse seine fisheries from 1992 to 1999. Vertebra centra were picked from 145 males and 153 females for age determination. The number of annual rings observed for males and females was 0–8 and 0–13, respectively. Combined sex von Bertalanffy growth equations were obtained as follows: L_t  = 216.4(1 − e^{−0.148( t +1.76)}) where L_t is precaudal length in cm at age t . A mature size for males was considered to be approximately 135–140 cm (precaudal length), with an estimated age of 5–6 years, whereas corresponding values for females were 145–150 cm and 6–7 years, respectively. Birth size ranged from 48 to 60 cm. There was no remarkable difference in growth, birth size and age at maturity between the Pacific and Atlantic Oceans. The life history parameters of the silky shark are approximately the same in both oceans.     

Models for forecasting sandfish catch in the coastal waters off Akita Prefecture and the evaluation of the effect of a 3-year fishery closure

SUMMARY: The sandfish Arctoscopus japonicus in the coastal waters off Akita Prefecture had been landed in amounts of more than 10 000 t continuously from 1963 to 1975. From 1976, however, it began to decrease sharply and fell to only 74 t in 1984. The fishery society of Akita Prefecture closed the fishing from 1 September 1992 to 30 September 1995. Since 1995, the total allowable catch (TAC) allocated in each year has increased. However, the mechanism behind the increment of catch has not been clearly demonstrated. The aim of this study is to elucidate the mechanism behind the increase of catch using catch forecasting models constructed with past water temperature and catch data. The results were as follows: (i) the effect of water temperature in the depth strata 200–300 m, September of year t –1, t –2 and t –3 of station 1 would be important for forecasting the catch in year t; (ii) coastal catch in year t –1 and t –2 would be important for forecasting the catch in year t; (iii) the effect of a fishery closure would be significantly related to the period of the closure and the environmental condition such as water temperature; and (iv) the TAC system would be important for the recovery of stock and to avoid the depletion of abundance.     

Size-related changes in habitat selection by larval grayling (Thymallus thymallus L.)

Abstract  – In a medium-sized river in northern Finland, larval grayling shifted with growth from shallow habitats with slow velocities, fine substrata and abundant vegetation cover to deeper sites with swifter velocities, coarse substrata and sparse vegetation cover within 3 weeks. Small (17–21 mm) larvae preferred water depths 10–30 cm, substrata dominated by mud or sand (<2 mm), 10–70% vegetation cover and water velocities <10 cm · s⁻¹. Middle-sized (22–25 mm) larvae preferred 30–90 cm depths, sandy substrata, <40% vegetation cover and velocities <10 cm · s⁻¹. Large (26–31 mm) larvae preferred >50 cm depths, substrata dominated by sand or boulders, <20% vegetation cover and 10–50 cm · s⁻¹ velocities. The strict habitat requirements of the smallest larval group suggest that these habitats, in particular, are important to the early survival of grayling.