Effects of different feeding level on the growth, feed efficiency and body composition of juvenile mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775)

The effects of several feeding levels (1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% and 4.5% of body weight per day, BW day⁻¹) on the growth, feed efficiency and body composition of juvenile Lutjanus argentimaculatus (body weight 27.1 g) were examined. Fish were fed a test diet (40% protein, 18.4% lipid and 13.4 kJ g⁻¹) for 75 days in three equal meals. Weight gain and specific growth rate increased with increasing feeding level up to 2.5% BW day⁻¹, after which no significant improvement in growth was observed. The feed efficiency, protein efficiency ratio, retention of protein and digestibility of nutrients did not differ for fish fed 1–2.5% BW day⁻¹, but decreased significantly when feeding levels were increased above 3% BW day⁻¹. The chemical compositions of whole fish or body organs were significantly affected by the feeding level. The condition factor, mesenteric fat, hepato- and viscerosomatic indices were higher in fish fed 2.5–4.5% BW day⁻¹. The cholesterol, triglycerides and haematocrit values were similar among treatments, except that high levels of plasma lipids were recorded in fish fed at 2.5% BW day⁻¹. Taking into consideration the growth, feed efficiency and body composition data attained in this study, a feeding level of 2.5% BW day⁻¹ is recommended for juvenile L. argentimaculatus weighing between 27 and 140 g.     

Fishery resources and economic gain in three mangrove areas on the south-east coast of India

Abstract The fishery resources and fishing income in three different mangrove areas were evaluated. The mangrove-rich area provided high catches of shellfish and finfish and yielded high fishery income, compared with the mangrove-poor areas. Luxuriant mangrove areas supported a catch of 11 kg shellfish ha⁻¹ day⁻¹ and 4.5 kg finfish ha⁻¹ day⁻¹, corresponding with an economic gain of US$ 14 (Rs 603.7) day⁻¹ for shellfish and US$ 3 (Rs 130.5) day⁻¹ for finfish. The value of maintaining mangroves to ensure better fishery resources and to support coastal economies was identified. Management practices for conserving and enhancing mangroves and associated fishery resources are suggested.     

The efficacy of emamectin benzoate as an oral treatment of sea lice, Lepeophtheirus salmonis (KrÒyer), infestations in Atlantic salmon, Salmo salar L.

The efficacy of emamectin benzoate as an oral treatment of sea lice, Lepeophtheirus salmonis (KrÒyer), infestations in Atlantic salmon, Salmo salar L., was evaluated in a dose titration study and two dose confirmation studies. Replicated groups of salmon with induced infestations of sea lice were given emamectin benzoate on pelleted feed at doses of 0, 25, 50 and 100 μg kg⁻¹ biomass day⁻¹ for seven consecutive days. Sea lice were counted at 7, 14 and 21 days from the start of treatment, and comparisons made with control fish given the same diet without emamectin benzoate. Total numbers of sea lice were significantly reduced at all doses in all three studies when compared to control fish. There was no significant difference between doses of 50 and 100 μg kg⁻¹, but the 50 μg kg⁻¹ dose resulted in significantly fewer lice than the 25 μg kg⁻¹ dose. Emamectin benzoate was highly effective in reducing numbers of preadult and adult lice and prevented the maturation of chalimus to motile stages. The optimum therapeutic dose was selected as 50 μg kg⁻¹ day⁻¹ for seven days. Treatment reduced the incidence of epidermal damage by sea lice and, in one study, survival of treated fish was 48% higher than in control groups. No fish mortalities or adverse effects were attributed to treatment with emamectin benzoate at any of the doses tested.     

Herpesviral haematopoietic necrosis virus (CyHV-2) infection: case studies from commercial goldfish farms

Herpesviral haematopoietic necrosis is a disease of goldfish, Carassius auratus , caused by Cyprinid herpesvirus-2 (CyHV-2) infection. Quantitative PCR was carried out on tissue homogenates from healthy goldfish fingerlings, broodfish, eggs and fry directly sampled from commercial farms, from moribund fish submitted to our laboratory for disease diagnosis, and on naturally-infected CyHV-2 carriers subjected to experimental stress treatments. Healthy fish from 14 of 18 farms were positive with copy numbers ranging from tens to 10⁷ copies μg⁻¹ DNA extracted from infected fish. Of 118 pools of broodfish tested, 42 were positive. The CyHV-2 was detected in one lot of fry produced from disinfected eggs. Testing of moribund goldfish, in which we could not detect any other pathogens, produced 12 of 30 cases with 10⁶–10⁸ copies of CyHV-2 μg⁻¹ DNA extracted. Subjecting healthy CyHV-2 carriers to cold shock (22–10 °C) but not heat, ammonia or high pH, increased viral copy numbers from mean copy number (±SE) of 7.3 ± 11 to 394 ± 55 μg⁻¹ DNA extracted after 24 h. CyHV-2 is widespread on commercial goldfish farms and outbreaks apparently occur when healthy carriers are subjected to a sharp temperature drop followed by holding at the permissive temperature for the disease.     

Growth of juvenile tilapia, Oreochromis niloticus L. from Lakes Zwai, Langeno and Chamo (Ethiopian rift valley) based on otolith microincrement analysis

Abstract – Age and growth of juvenile tilapia, Oreochromis niloticus , from Lakes Zwai, Langeno and Chamo (Ethiopia) were studied from microincrements in otoliths. Growth in length was best described by the Gompertz model. Average growth rate of the fish was most rapid in Lake Chamo (0.39 mm  ·  day⁻¹, 1.14%  ·  day⁻¹), intermediate in Lake Zwai (0.20 mm  ·  day⁻¹, 0.72%  ·  day⁻¹) and slowest in Lake Langeno (0.16 mm  ·  day⁻¹, 0.62%  ·  day⁻¹). Similarly, back-calculation from otolith increment widths gave growth rates of 0.28 to 0.43 mm  ·  day⁻¹, 0.15 to 0.32 mm  ·  day⁻¹ and 0.11 to 0.28 mm  ·  day⁻¹ for Chamo, Zwai and Langeno fish, respectively. In addition, Fulton's condition factor was largest for Chamo tilapia and smallest for Langeno tilapia; the difference between fish from Langeno and Zwai was small. Rapid growth of juvenile O. niloticus in Lake Chamo was attributed to warm temperature and better food quality. ^Note     

Evaluation of lipid spray beads for the delivery of water-soluble materials to a marine suspension-feeder, the Manila clam Tapes philippinarum (Deshayes 1853)

We describe the development and evaluation of a new microparticle for delivering low-molecular weight, water-soluble materials to suspension feeders. Spray beads successfully incorporated materials dissolved in an aqueous phase or as dry particulate, within a triacylglyceride bead composed of tripalmitin, 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ triolein, or 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ fish oil.
Riboflavin was successfully incorporated (up to 44 mg g⁻¹ lipid) and retained (up to 98% over 24 h in seawater) as dry particles in all three mixtures of lipid. Aqueous oxytetracycline hydrochloride or polymeric dye were incorporated (45.6 mg g⁻¹ lipid and 18.1 mg g⁻¹ lipid, respectively) and retained best (99% and 94%, respectively) in spray beads composed of tripalmitin. The addition of triolein or fish oil to the lipid bead reduced incorporation and retention efficiencies for aqueous core materials by up to 75%.
Manila clam seed readily ingested and digested lipid microparticles, spray beads and lipid-walled microcapsules. Microparticles composed of tripalmitin were excreted with their payloads intact. Intact microparticles composed of 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ fish oil were largely absent in faecal strands suggesting successful release and delivery of microparticle contents to clams.
Spray beads composed of tripalmitin softened with 400 mg g⁻¹ fish oil represent an effective microparticle type for delivering low-molecular weight, water-soluble materials to aquatic suspension feeders.     

Comparative performance of juvenile red abalone, Haliotis rufescens, reared in laboratory with fresh kelp and balanced diets

Juvenile Haliotis rufescens were reared in the laboratory in order to investigate the extent to which fresh kelp and formulated feeds with 250 g kg⁻¹ (25P) and 380 g kg⁻¹ protein content (38P) affected their growth rate, gut residence time (GRT), food consumption ( C ), food conversion ratio (FCR) and digestibility. Abalone from 38P attained the highest growth rate (70.5 ± 4.2 μm day⁻¹; 98.3 ± 6.95 μg day⁻¹), followed by 25P (47.9 ± 2.79 μm day⁻¹; 67.4 ± 2.82 μg day⁻¹) and kelp (23.6 ± 3.36 μm day⁻¹; 28.2 ± 4.11 μg day⁻¹). No significant differences were observed in consumption rate among treatments (0.61–0.68% body weight per day), yet kelp-fed abalone exhibited higher FCR (2.44), protein efficiency ratio (4.42), and apparent digestibility of dry matter (69.5%), protein (69.8%) and gross energy (79.2%) than 38P organisms (59.8, 62.4 and 62.2%, respectively). They also showed longer GRT (23.1 ± 0.93 h). This study demonstrated that formulated diets with 250 g kg⁻¹ and 380 g kg⁻¹ protein inclusion can sustain higher growth rates of juvenile H. rufescens than fresh algae. These differences seem to be due to the amount of dietary protein. Kelp meal appears to improve the consumption and digestibility of balanced diets, and its inclusion in formulated diets is recommended.     

Patterns of growth of juvenile pink abalone Haliotis corrugata fed re-hydrated natural feeds at a laboratory and a hatchery

The feasibility of obtaining a similar growth response from juvenile pink abalone Haliotis corrugata at a research laboratory and a hatchery, when using natural feeds was evaluated. Four macroalgae, Egregia menziesii , Eisenia arborea , Macrocystis pyrifera , Gracilaria sp., and the surfgrass Phyllospadix torreyi were used as feeds. Response patterns of abalone were very similar at both facilities in terms of final length, weight, and survival, varying from 13.0 to 15.50 mm, 0.31 to 0.52 g, and 60.0% to 78.6%, respectively. Better growth was obtained when E. menziesii , M. pyrifera , and Gracilaria sp. were offered. Poor results were obtained with surfgrass. The feed conversion ratio was determined at the laboratory and did not vary significantly, ranging from 42.3 to 199.0; although a significant inverse correlation was observed with growth rate. Growth in length and weight and survival rates varied within 1.6–20.2 μm day⁻¹, 0.123–1.664 mgday⁻¹, 0.4–0.64%day⁻¹, respectively. Mean growth rate in length (14.7μm day⁻¹) and weight (1.18 mg day⁻¹) at the hatchery were significantly higher than that obtained at the laboratory (9.4 μm day⁻¹ and 0.77 mg day⁻¹), which is most likely a consequence of more suitable water temperature at the hatchery. Mean survival rate was significantly higher at the laboratory (53.1%day⁻¹) than at the hatchery (46.1%day⁻¹).     

Effects of Rhizopus extract administration on somatic growth and sexual maturation in lacustrine sockeye salmon Oncorhynchus nerka

ABSTRACT: The filamentous fungi Rhizopus , like many fungal species, possesses physiologically active substances. Rhizopus extract (RU) is reported to be effective for various aspects of growth and reproduction in many vertebrates. The effects of RU administration on body growth and plasma levels of steroid hormones were investigated in lacustrine sockeye salmon Oncorhynchus nerka . One-year-old fish were fed daily with RU (20 mg/kg feed) from July 1999 to October 2000 for 15 months. Fish were sampled every month and plasma levels of testosterone (T), 11-ketotestosterone (11-KT), estradiol-17β (E₂) and 17α,20β-dihydroxy-4-pregnen-3-one (DHP) were measured by time-resolved fluoroimmunoassay. Body growth of RU-fed fish of both sexes increased significantly in 1⁺ and 2⁺ October, and 2⁺ January–March and July. All RU-fed males and one female matured in 2⁺ October. RU-fed 1⁺ precociously mature males showed increased plasma levels of T, 11-KT and DHP in 1⁺ October. In 2⁺ males, RU significantly elevated plasma levels of T from May to June, 11-KT from June to July, and DHP in October. In sockeye salmon, administration of RU accelerated body growth of both sexes and sexual maturation in males, suggesting physiologically active substances present in RU enhance somatic growth and sexual maturation by sex-specific mechanisms.     

The potential of liposomes as a nutrient supplement in first-feeding marine fish larvae

The ingestion rate (ng liposome larva^–1 h^–1) of extruded [1–¹⁴C] palmitic acid-labelled liposomes containing physiological saline (PHS) or cod fish extract (CFE), was tested in 5-day-old gilthead seabream Sparus aurata and white grouper Epinephelus aeneus larvae. A follow-up study compared the assimilation of radioactive free fatty acid (FFA) label of these two liposome treatments into six phospholipid and neutral lipid fractions as well as the nonlipid fraction in 5-day-old seabream. In seabream larvae, there was a 50-fold ( P  < 0.05) increase in the net consumption rate when fed CFE liposomes (2305.8 ng liposome larva^–1 h^–1) compared with liposomes containing physiological saline (42.7 ng liposome larva^–1 h^–1). A similarly significant ( P  < 0.05) but less marked pattern was also observed in the grouper larvae where the CFE treatment larvae ingested 238.5 ng liposome larva^–1 h^–1 compared with 54.3 ng liposome larva^–1 h^–1 in larvae fed the PHS liposomes. In seabream larvae ingesting CFE and PHS liposomes, radioactivity was found in all larval fractions analysed. However, marked treatment differences ( P  > 0.05) in assimilation were found only in the triacylglycerol fraction (3.4 and 0.6 dpm larva^–1 h^–1, respectively) and nonlipid fraction (11.2 and 15 dpm larva^–1 h^–1, respectively).     

Dynamic in-lake spawning migrations by female sockeye salmon

Abstract –  Precise homing by salmon to natal habitats is considered the primary mechanism in the evolution of population-specific traits, yet few studies have focused on this final phase of their spawning migration. We radio tagged 157 female sockeye salmon ( Oncorhynchus nerka ) as they entered Lake Clark, Alaska, and tracked them every 1–10 days to their spawning locations. Contrary to past research, no specific shoreline migration pattern was observed (e.g., clockwise) nor did fish enter a tributary unless they spawned in that tributary. Tributary spawning fish migrated faster (mean = 4.7 km·day⁻¹, SD = 2.7, vs. 1.6 km·day⁻¹, SD = 2.1) and more directly (mean linearity = 0.8, SD = 0.2, vs. 0.4, SD = 0.2) than Lake Clark beach spawning fish. Although radio-tagged salmon migrated to within 5 km of their final spawning location in an average of 21.2 days (SD = 13.2), some fish migrated five times the distance necessary and over 50 days to reach their spawning destination. These results demonstrate the dynamic nature of this final phase of migration and support studies indicating a higher degree of homing precision by tributary spawning fish.     

Short-term dietary supplementation with the microalga Parietochloris incisa enhances stress resistance in guppies Poecilia reticulata

Two trials were conducted to determine the effects of dietary enrichments with the microalga Parietochloris incisa , rich in arachidonic acid (ARA), on stress resistance in guppies Poecilia reticulata . The microalga was added to commercial diets as a neutral lipid (NL) extract and its fractions or as broken cells. Experimental diets were applied for a period of 14 days. In trial 1, commercial diets were supplemented with NL (containing 25 mg ARA and 0.11 mg β-carotene g⁻¹ feed), its triacylglycerol (TAG) fraction (containing 25 mg ARA g⁻¹ feed and no β-carotene) and the β-carotene fraction (containing 0.11 mg carotenoid g⁻¹ feed and minute amounts of ARA). Neutral lipid-fed fish demonstrated the highest resistance ( P <0.05) to osmotic stress (32-ppt NaCl), followed by fish fed with diets supplemented with TAG and β-carotene alone, which were more resistant than control ( P <0.05). In trial 2, fish fed diets supplemented with higher levels of broken alga (26.1 mg ARA g⁻¹ feed) were more resistant ( P <0.05) to stress as compared with fish fed lower ARA (16.3 mg g g⁻¹) or an unsupplemented control diet. We suggest a dietary supplementation with broken P. incisa cells to enhance stress resistance in guppies before a stressful event.     

Comparison of lipid-walled microcapsules and lipid spray beads for the delivery of water-soluble, low-molecular-weight materials to aquatic animals

Microparticles (< 40 μm diameter) composed of 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ fish oil were used to encapsulate the low-molecular-weight (mol. wt 460) antibiotic oxytetracycline in the form of either oxytetracycline hydrochloride (OTC.HCl) or oxytetracycline hemicalcium salt (OTC.HEM). Dry, finely ground particles of core material were encapsulated in spray beads. Dissolved core material was encapsulated in lipid-walled microcapsules.
Oxytetracycline (OTC) was most efficiently delivered (≈ 46.5 mg g⁻¹ lipid after 24 h suspension in seawater) as a hemicalcium salt in spray beads. Lipid-walled microcapsules were most efficient for delivering OTC (≈ 8.7 mg g⁻¹ lipid) as OTC.HCl dissolved in 0.2  M HCl at a concentration of 300 mg mL⁻¹.
Spray beads containing OTC.HEM were very stable over 1 month in storage. Lipid-walled microcapsules containing aqueous OTC.HCl lost ≈ 30% of their core material during storage. Freeze-drying of both microparticle types did not improve storage of spray beads, but showed promise for reducing leakage from lipid-walled microcapsules during storage and delivery to suspension feeders.     

Infectious pancreatic necrosis virus: experimental infection of goldsinny wrasse, Ctenolabrus rupestris L. (Labridae)

The use of wrasse as cleaner fish in farming of Atlantic salmon, Salmo salar L., is now widespread in Scotland, Ireland and Norway, but little is known about the susceptibility of these fish to the common pathogens of cage-cultured salmon. The susceptibility of goldsinny wrasse, Ctenolabrus rupestris L., to infectious pancreatic necrosis virus (IPNV) was investigated. Captive-bred C. rupestris were infected with IPNV-Sp (Shetland strain) using a bath challenge method. Two infection doses were used, low (4.1 × 10⁵ pfu mL⁻⁻¹) and high (2.4 × 10⁶ pfu mL⁻⁻¹), with two replicates for each experiment. Bathing times were 1 h for the low dose and 5 h for the high dose. A maximum prevalence of infection (30%) was seen 2 weeks post-infection in replicate 1 of the low dose experiment and was accompanied by low tissue titres. The tissue titres dropped to an undetectable level by 4 weeks post-infection. In the high dose experiment, a high prevalence of infection was seen along with moderate titres in tissues as well as a marked pathological response. Both prevalence and intensity declined rapidly and the fish recovered. In the high dose experiment, faecal titres followed the same pattern as those in the tissues. The implications for the use of wrasse in the farming of Atlantic salmon are discussed.     

Cryopreservation of Sperm of Farmed European Eel Anguilla anguilla

Sexual maturation and sperm release were induced in farmed European eels Anguilla anguilla kept exclusively in fresh water by using two dosages of human chorion gonadotropin (100 International Unit (IU)-Group one and 250 IU/individual per week-Group two). Sperm release took over 13 wk in both groups. The quality of sperm was investigated on the eighth, ninth, and tenth wk. The average cell densities were 0.94 ± 0.4 × 1010 (Group one) and 0.93 to. ± 0.6 × 10¹⁰ (Group two) spermatozoa/mL. The estimated motility of eel sperm was 33, 55, and 49% on the eighth, ninth, and tenth wk of treatment, respectively. The estimated average motility of samples selected for cryopreservation was 73 ± 10%, while the post-thaw motility of cryopreserved samples was 36 ± 11%. The extender originally developed for common carp sperm crypreservation together with methanol as cryoprotectant was found suitable for the cryopreservation of European eel sperm.     

Continuous exposure to infectious pancreatic necrosis virus during early life stages of rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout, Oncorhynchus mykiss (Walbaum), were exposed continuously to infectious pancreatic necrosis virus (IPNV) at 0, 10¹, 10³ or 10⁵ plaque forming units (pfu) L⁻¹ of water to estimate the effects of chronic IPNV exposure on early life stages. Fish density averaged 35 fish L⁻¹ (low density) or 140 fish L⁻¹ (high density), and the tank flow rate was 250 mL⁻¹ min. Virus exposure began at 6 days before hatch and continued until fish were 44 days old. Cumulative per cent mortality, analysis of survival and hazard functions, and discrete-time event analysis were used to explore the patterns of survival and mortality. In eggs and fish exposed to IPNV, mortality significantly greater than in the 0 pfu L⁻¹ exposure did not occur until IPNV concentration was 10⁵ pfu L⁻¹ at low fish density and 10³ pfu IPNV L⁻¹ at high fish density. These results suggest that in the natural aquatic environment, where rainbow trout densities are likely to be considerably lower than in this study, mortality resulting from infection with IPNV will very likely not occur when ambient concentrations of virus are ≤10³ pfu IPNV L⁻¹. In aquaculture rearing units, trout density is likely to be as high or higher than the densities used in this study. Therefore, continuous inputs of virus at concentrations greater than 10¹ pfu L⁻¹ may result in IPN epidemics in aquaculture facilities.     

Perception of light intensity by Haliotis discus discus based on locomotor activity patterns

ABSTRACT:   An apparatus to measure the locomotor activity of aquatic benthic organisms at variable low light levels was developed and the diurnal behavioral pattern of the abalone Haliotis discus discus was measured at various low light intensities. During the experiment, abalone were exposed to 12 h light–dark cycles of complete darkness, 0 µmol/m²/s throughout the 12 h dark cycle and, during periods I (days 1–8) and III (days 19–26), the 12 h light cycles were set at 10 µmol/m²/s. During period II (days 10–17), abalone were exposed to a light level during the 12 h light cycles of 1 × 10⁻⁵, 1 × 10⁻⁶, 1 × 10⁻⁷ or 1 × 10⁻⁸ µmol/m²/s and the changes in locomotor activity assessed. At daytime levels of 1 × 10⁻⁵ µmol/m²/s, typical behavioral patterns were observed of high locomotory activity during the night-time cycle. However, at lower light intensities, the distinction between day and night activity patterns became less clear and, at intensities lower than 1 × 10⁻⁷ µmol/m²/s, the difference between activity during the light and dark cycles became negligible. Based on this, we conclude that the threshold of light level perception in relation to locomotor activity is approximately 1 × 10⁻⁷ µmol/m²/s. The significance of these results in relation to the entrainment of behavior in abalone is discussed.     

Seasonal variation in body composition of Arctic char, Salvelinus alpinus, from an ultraoligotrophic alpine lake

Abstract  – Seasonal pattern of energy content was determined in a population of Arctic char, Salvelinus alpinus (L.), living in an ultraoligotrophic alpine lake (altitude 1100 m) located in central Norway (62°5'N). Specific somatic energy content varied between 4.3 and 6.1 kJ · g⁻¹ in spawners and between 4.8 and 6.6 kJ · g⁻¹ in immatures. Corresponding values for specific somatic lipid energy were 0.5–1.6 kJ · g⁻¹ for spawners and 0.7–2.1 kJ · g⁻¹ for immatures. The temporal pattern in storage energy residuals (deviation from mean storage energy, all sampling periods pooled) indicated that total, protein and lipid energy accumulated in the autumn and early winter. This increase was followed by a winter decrease in somatic energy (January to April). A new increase in total somatic energy and somatic lipid energy occurred during late winter (March/April to June), while the lake was still ice covered and water temperatures ranged between 0.5 and 2.5 °C. The observed seasonal pattern of specific energy storage and lipid deposition demonstrated a considerable potential for energy accumulation in Arctic char at low temperatures. It is discussed whether freshwater lakes at high altitudes or latitudes represent a temperature-stabilised and predictable environment in contrast to the variable temperature experienced in the corresponding terrestrial system.     

Field observations and laboratory experiments on growth and lipid content of young-of-the-year perch

Abstract –  Differences in growth and allocation of energy of young-of-the-year (YOY) perch ( Perca fluviatilis ) were studied in relation to both quantity and quality of food. Feeding on fish and Mysidacea, the mean size of YOY perch after the first growing season in Lake Pfeiffer was 152 mm. In contrast, YOY perch grew to 107 mm in Lake Speldrop and 83 mm in Lake Reeser Meer while mainly feeding on zooplankton. In correlation with food uptake and growth, the lipid content of YOY perch was significantly highest in Lake Pfeiffer and lowest in Lake Reeser Meer, assuming that YOY perch from Lake Pfeiffer should be able to survive starvation periods during their first winter better then those from Lake Speldrop and Lake Reeser. While feeding on fish, mean highest growth rates were 1.31 mm·day⁻¹ in the laboratory. Growth in weight started when food uptake exceeded 66 J·g WW⁻¹·day⁻¹, while an increase of lipid content required food input of 175 J·g WW⁻¹·day⁻¹. Increased growth potential associated with the availability of energetically profitable food is assumed as an important factor that could have far-reaching consequences for the fish community.     

Survival and movement of hatchery-reared red snapper on artificial habitats in the northern Gulf of Mexico

Abstract  Hatchery-reared age-0 red snapper, Lutjanus campechanus (Poey), were released onto artificial habitats in the Gulf of Mexico. Fish showed 12.7% survival after 7 months on small habitats (0.86 m³) and 3.1% survival after 8 months on large habitats (3.9 m³). Emigration was estimated by the movement of fish to unstocked habitats and accounted for 76.8% of the total decline in abundance at release sites after 26 days. Fish showed higher survival and growth rates on small habitats (27.6% at 26 days; 0.33 mm day⁻¹) compared with large habitats (13.2% at 34 days; 0.26 mm day⁻¹), which may have been due to increased predation and competition on large habitats. Fish became evenly distributed among adjacent habitats 26 days after release, indicating that stocking densities at release habitats were above carrying capacities. These observations suggested that providing additional habitat around red snapper release sites would increase survival.