Maturity, ovarian cycle, fecundity, and age-specific parturition of black rockfish (Sebastes melanops)

From 1995 to 1998, we collected female black rockfish (Sebastes melanops) off Oregon in order to describe their basic reproductive life history and determine age-specific fecundity and temporal patterns in parturition. Female black rockfish had a 50% probability of being mature at 394 mm fork length and 7.5 years-of-age. The proportion of mature fish age 10 or older significantly decreased each year of this study, from 0.511 in 1996 to 0.145 in 1998. Parturition occurred between mid-January and mid-March, and peaked in February. We observed a trend of older females extruding larvae earlier in the spawning season and of younger fish primarily responsible for larval production during the later part of the season. There were differences in absolute fecundity at age between female black rockfish with prefertilization oocytes and female black rockfish with fertilized eggs; fertilized-egg fecundity estimates were considered superior. The likelihood of yolked oocytes reaching the developing embryo stage increased with maternal age. Absolute fecundity estimates (based on fertilized eggs) ranged from 299,302 embryos for a 6-year-old female to 948,152 embryos for a 16-year-old female. Relative fecundity (based on fertilized eggs) increased with age from 374 eggs/g for fish age 6 to 549 eggs/g for fish age 16.

Small-scale spatial and temporal variability in growth and mortality of fish larvae in the subtropical northcentral Gulf of Mexico: implications for assessing recruitment success

Extensive plankton collections were taken during seven September cruises (1990–93) along the inner continental shelf of the northcentral Gulf of Mexico (GOM). Despite the high productivity and availability of food during these cruises, significant small-scale spatial variability was found in larval growth rates for both Atlantic bumper (Chloroscombrus chrysurus, Carangidae) and vermilion snapper (Rhomboplites aurorubens, Lutjanidae). The observed variability in larval growth rates was not correlated with changes in water temperature or associated with conspicuous hydrographic features and suggested the existence of less-recognizable regions where conditions for growth vary. Cruise estimates of mortality coefficients (Z) for larval Atlantic bumper (n=32,241 larvae from six cruises) and vermilion snapper (n= 2581 larvae from four cruises) ranged from 0.20 to 0.37 and 0.19 to 0.29, respectively. Even in a subtropical climate like the GOM, where larval-stage durations may be as short as two weeks, observed variability in growth rates, particularly when combined with small changes in mortality rates, can cause order-of-magnitude differences in cumulative larval survival. To what extent the observed differences in growth rates at small spatial scales are fine-scale “noise” that ultimately is smoothed by larger-scale processes is not known. Future research is needed to further characterize the small-scale variability in growth rates of larvae, particularly with regard to microzooplankton patchiness and the temporal and spatial pattern of potential predators. Small-scale spatial variability in larval growth rates may in fact be the norm, and understanding the implications of this subtle mosaic may help us to better evaluate our ability to partition the causes of recruitment variability.

Current velocity and catch efficiency in sampling settlement-stage larvae of coral-reef fishes

Light traps and channel nets are fixed-position devices that involve active and passive sampling, respectively, in the collection of settlement-stage larvae of coral-reef fishes. We compared the abundance, taxonomic composition, and size of such larvae caught by each device deployed simultaneously near two sites that differed substantially in current velocity. Light traps were more selective taxonomically, and the two sampling devices differed significantly in the abundance but not size of taxa caught. Most importantly, light traps and channel nets differed greatly in their catch efficiency between sites: light traps were ineffective in collecting larvae at the relatively high-current site, and channel nets were less efficient in collecting larvae at the low-current site. Use of only one of these sampling methods would clearly result in biased and inaccurate estimates of the spatial variation in larval abundance among locations that differ in current velocity. When selecting a larval sampling device, one must consider not only how well a particular taxon may be represented, but also the environmental conditions under which the device will be deployed.

A study on damage caused to crustacean and finfish larvae during collection of Penaeus monodon (Fab.) postlarvae in the estuaries of Barguna, Bangladesh

A year round investigation in the estuaries of Barguna district revealed that for each Penaeus monodon postlarvae (PL), about 37 larvae of other shrimp species, 12 finfishes and 10 macrozooplankters are destroyed during the process of shrimp seed collection. Although abundance of P. monodon PL was not recorded throughout the year, a significant number of other shrimp spp., fin fishes including macrozooplankters are being damaged by the shrimp seed collectors. This indiscriminate destruction of aquatic organisms during P. monodon PL collection is serious threat to aquatic biodiversity.

Rearing of catfish (Clarias batrachus Lin.) larvae with live and prepared feeds

Provision or live feed (Tubificid worms) attributed significantly better weight gain in the five days old Clarias batrachus larvae when reared for another 28 days compared to those fed mixed feed (live and artificial) and artificial feed only. Larvae fed mixed feed showed significantly better weight gain compared to those fed only artificial feed and the survival rate was similar to those fed only live feed. Both the weight gain and survival rate were the lowest for the larvae reared only on artificial feed.

Growth and survival of Clarias batrachus (Lin.) larvae fed on formulated diets

An experiment was conducted for a period of 28 days using 7-day old C. batrachus larvae of initial total length (±S.D.) of 7.4 ± 0.49 mm and weight (±S.D.) of 2.8 ± 0.75 mg. Five test diets viz. diets I, II, III, IV and V were prepared. Diet I was formulated using 30% fish meal (FM), 20% soybean meal (SM) and 20% Baker's yeast (BY), diet III using 15% FM, 20% SM, 15% cotton seed meal and 30% BY and diet IV using 20% FM, 30% BY and 30% powdered milk. The remaining two diets (diets II and V) were prepared using minced clam meat (96%) and BY (90%) respectively as the sole source of protein. Three replications were used for each treatment. The larvae fed on diet II exhibited significantly (P<0.05) better length gain and specific growth rate (SGR) than those of the larvae fed on diet III and there was no significant difference among the length gain and SGR of the larvae fed on diet I,II,IV and V. The larvae fed on diet II also showed significantly better weight gain and survival than those of the larvae fed on other diets. There was no significant difference between the condition factor of the larvae fed on diet II and IV. However, the larvae fed on diet II showed better condition factor than those of the larvae fed on other diets.

Colossal loss of shell and fin-fish larvae during collection of Penaeus monodon (Fab.) fry in the rivers of Satkhira

This study was conducted in five river-estuaries of Satkhira from January to December '96. It was found that during the collection of each Peneaus monodon) post larva (PL), about 45 larvae of other shrimps, 12 individuals of fin-fishes and 530 macro-zooplankters were mercilessly destroyed. It was also recorded that about 11.6 million of P. monodon PLs were harvested annually from the study area. The sh1dy implies that colossal loss of shell and fin-fishes and other plankton resources is done by tiger shrimp fry collectors, and such massive destruction adversely affect the natural productivity and ecological balance of the coastal environment.

Dietary cholesterol requirement of larvae and postlarvae of the prawn Penaeus indicus (H. Milne Edwards)

Two sets of experiments were conducted to determine the dietary cholesterol requirement of larvae and postlarvae 1-10 of Penaeus indicus. Seven approximately isocaloric and isonitrogenous purified experimental diets were tried with graded levels of cholesterol ranging from 0 to 4%. The control feed for larvae and postlarvae 1-10 were phytoplankton and compounded feed NPCL-17, developed by CMFRI, Cochin respectively. Result of these experiments indicates that cholesterol is an essential nutrient in the diet of larvae and postlarvae 1-10. Survival and growth of larvae and postlarvae 1-10 were greatly affected by cholesterol deficiency in the diet. The optimal cholesterol requirement for larvae appeared to be 0.5% of the diet, while it was higher for postlarvae where inclusion of cholesterol at a level of 2% in the diet gave higher growth.

Bothid larvae (Pleuronectiformes-pisces) of the Gulf od Thailand and South China Sea

The larvae of bothids were found to be sparsely distributed in the Gulf of Thailand and South China Sea being only 11.9% in the Naga Expedition Collections. They were confined mostly to the coastal waters and were found in near shore stations situated between Bangkok and Saigon. Their density was high in the Gulf of Thailand. The larvae seem to prefer darkness with greater incidence during April 16 to October 15 period, with a peak in the collections taken during April. This report includes the occurrence of 17 species belonging to 6 genera collected from the Gulf of Thailand and South China Sea, along with their regional, seasonal as well as diurnal variations

Results of the Austrian-Ceylonese hydrobiological mission 1970 of the 1st Zoological Institute of the University of Vienna (Austria) and the Department of Zoology of the Vidyalankara Campus of the University of Ceylon. Pt. 11. Larvae and pupae of water beetles collected from the islands of Ceylon

Water beetle larvae and pupae were collected from the lotic biotopes in localities of the southern part of Ceylon. The species are described and findings are related to previous investigations. The following families were represented: Dytiscidae, Gyrinidae, Hydrophilidae, Helodidae, Dascillidae (Eubrianacinae), Dryopidae and Lampyridae.

Results of the Austrian-Ceylonese hydrobiological mission 1970 of the 1st Zoological Institute of the University of Vienna (Austria) and the Department of Zoology of the University of Ceylon Vidyalankara Campus, Kelaniya. Pt. 12. Contributions to the ecology of the larvae of some Odonata from Ceylon

The Austrian-Ceylonese hydrobiological mission studied 38 biotopes; 28 of which contain Odonata. From the Zygoptera the Calopterydoidea seem to be the dominant form (22 habitats), while the Coenagrionoidea are scarcer (11 habitats). The most frequent species was Euphaea splendens (Epallagidae - 16 habitats) followed by Vestolis apicalis nigrescens (Calopterygidae, 8 habitats) and Neurobasis chinensis (Calopterygidae, 6 habitats). From the Anisoptera Zygonyx ceylanica (Libellulidae: Zygonictinae) was the dominant form (8 habitats), but some Libellulinae remain undescribed. The number of species varied greatly between different biotopes. The biotopes containing Odonata are small brooks, in which the pH was mostly on the limit between acid and alkaline reaction. They are fast running waters, situated in most cases on lower or middle elevations, only three species being found in higher elevations (1800-2000 m). Adaptations to fast currents and other factors are described.

Effect of combined thyroxine and cortisol treatment on hatching of eggs, post-embryonic growth and survival of larvae of Heteropneustes fossilis

In order to record the effects of thyroxine and cortisol (individual/combined) on hatching, post-embryonic growth and survival of larvae of Heteropneustes fossilis, newly fertilized eggs were given bath immersion treatments of L-thyroxine (T sub(4); 0.05 mg/l), cortisol (0.50 mg/l) and T sub(4)+ cortisol (0.05 mg/l+0.50 mg/l) for 15 days. Hatching of eggs, growth and survival of the larvae improved significantly (P<0.001) in the hormone treated groups as compared to those of control. The frequency of deformities was reduced in the combined hormone treatment group. The present observations suggest that the advanced digestive function probably induced by T sub(4)+cortisol treatment might have resulted in improvement in food utilization during the critical phases of first feeding and promoted vital developmental processes resulting in uniform growth, decreased mortality, better survival and transformation of larvae to juveniles. This combined hormone therapy appears to have practical utility in fish hatchery practice for better success in larval rearing.