Effects of temperature on the biology of the northern shrimp, Pandalus borealis, in the Gulf of Maine

Length-frequency data collected from inshore and offshore locations in the Gulf of Maine in 1966-1968 indicated that ovigerous female northern shrimp (Pandalus borealis) first appeared offshore in August and September and migrated inshore in the fall and winter. Once eggs hatched, surviving females returned offshore. Juveniles and males migrated offshore during their first two years of life. Sex transition occurred in both inshore and oll'shore waters, but most males changed sex offshore during their third and fourth years. Most shrimp changed sex and matured as females for the first time in their fourth year. Smaller females and females exposed to colder bottom temperatures spawned first. The incidence of egg parasitism peaked in January and was higher for shrimp exposed to warmer bottom temperatures. Accelerated growth at higher temperatures appeared to result in earlier or more rapid sex transition. Males and non-ovigerous females were observed to make diurnal vertical migrations, but were not found in near- surface waters where the temperature exceeded 6°C. Ovigerous females fed more heavily on benthic molluscs in inshore waters in the winter, presumably because the egg masses they were carrying prevented them from migrating vertically at night. Northern shrimp were more abundant in the southwestern region of the Gulf of Maine where bottom temperatures remain low throughout the year. Bottom trawl catch rates were highest in Jeffreys Basin where bottom temperatures were lower than at any other sampling location. Catch rates throughout the study area were inversely related to bottom temperature and reached a maximum at 3°C. An increase of 40% in fecundity between 1973 and 1979 was associated with a decline of 2-3°C in April-July offshore bottom temperatures. Furthermore, a decrease in mean fecundity per 25 mm female between 1965 and 1970 was linearly related to reduced landings between 1969 and 1974. It is hypothesized that temperature-induced changes in fecundity and, possibly, in the extent of egg mortality due to parasitism, may provide a mechanism which could partially account for changes in the size of the Gulf of Maine northern shrimp population during the last thirty years. (PDF file contains 28 pages.)

Welche Faktoren beeinflussen die Stärke der Dorsch-Jahresklassen?

In the previous years extensive investigations were carried out concerning the reproduction biology of cod in the Baltic Sea. The analyses showed that the year class strength of the eastern Baltic cod stock is decisively determined by the bad oxygen conditions during the spawning season in the summer and by sprat as predator of the cod eggs. In the western Baltic Sea these factors have no importance. The year classes are mainly determined by the strong variations of the portions of female cods, which participated in the spawning activities in the region. The individuals within the length range from 35 cm to 45 cm have a special importance at this time, caused by the actual age structure of the cod stock.

Length-weight relationship and the diets of Clarias lazera (Cuvier and Valenciennes), family Clariidae (Osteichthyes: Siluriformes) in Zaria, Nigeria

The length-weight relationship and the diets of Clarias lazera were investigated between July 1981 and June 1982. About 450 specimens were examined. The standard lengths of the fish ranged from 8.5 cm to 42.2 cm. Significant differences were found between the standard lengths of the males and females with the latter slightly shorter. Somatic weights varied between 10 g to 502 g. Length-weight regression analysis gave a "b" value of 3.02 for both males and females combined; thus indicating an isometric growth. Analysis of the food in the stomachs showed that the fish is an omnivore although, it fed more on insects and fish than other food items

A study of the length at maturity and hooks/gill net mesh selection in Clarias lazera from Lake Chad

The minimum length at first maturity of Clarias lazera was found to be 24 cm (4.8%) for females and 20 cm (1.8%) for males. Fifty percent maturity was attained at length of 28 cm to 30 cm for both sexes; there being little difference among the sexes at this level of maturity. The modal retention lengths for gill nets were: 13 cm for 25.5 mm mesh; 18 cm for 32 mm mesh; 28 cm for 57 mm mesh; and 38 cm for 76 mm mesh. Modal lengths of Clarias lazera caught by various hooks sizes were No. 10 (28 cm); No. 11 (33 cm); Nos. 15 and 16 (28 cm). It is recommended that to protect the clarias fishery in Lake Chad, the use of gill nets of less than 57 mm mesh size and fishing hook No. 16 (and smaller sizes) which caught 43.94% of immature fishes should be discouraged

Age and growth of Heterotis niloticus around Pategi in the middle River Niger, Kwara State

Biological studies of Heterotis niloticus were conducted for three years in the middle River Niger. Scales were found to be the most suitable structure in ageing Heterotis which was validated by length/histogram curve. Annual rings were found to be formed between March to June. Growth was rapid in the first two years and they reached sexual maturity at 2 years. The male grow longer while the female are bulkier. The length-weight relationship of male and female Heterotis did not differ significantly and the resulting equation for male was W = 1.25L super(2.5) and W = 1.6L super(2.7) for females respectively where W = weight (g) and L = total length. The total length to body scale relationship was found to be L = 14.3R super(2.6) where (R = oral radius of scale Heterotis growth was found to be allometric

Length-frequency estimation for yellowfin tuna (Thunnus albacares) caught by commercial fishing gear in the Eastern Pacific Ocean

ENGLISH: Methods of collecting samples for the purpose of estimating the numbers and weights of fish caught, by length interval, are described. Several models for two-stage sampling are described, and the equations for the estimators and their variances are given. The results from a brief simulation study are used to show the differences between estimates made with the different models. Estimators for the average weights of fish in the catch and their variances are also described. These average weights are used to provide improved estimates of the total annual catches of yellowfin taken from the eastern Pacific Ocean, east of 150°W, between 1955 and 1990. SPANISH: Se describen los métodos de recoger de muestreo para estimar el número o peso de peces capturados, por intervalo de talla. Se describen varios modelos para el muestreo de dos etapas, y se presentan las ecuaciones para los estimadores y sus varianzas. Se usan los resultados de un breve estudio de simulación para indicar las diferencias entre estimaciones realizadas con los distintosmodelos. También se describe un estimador para el peso promedio de peces en la captura y su varianza. Se usan estos estimadores para calcular estimaciones mejoradas de las capturas anuales totales de aleta amarilla tomadas del Océano Pacífico oriental, al este de 150°W, entre 1955 y 1990. (PDF contains 41 pages.)

Growth and age composition of northern bluefin tuna, Thunnus thynnus, caught in the Eastern Pacific Ocean, as estimated from length-frequency data, with comments on trans-Pacific migrations

ENGLISH: The spawning of Pacific northern bluefin tuna, Thunnus thynnus, takes place only in the western Pacific Ocean (WPO), but substantial numbers of the juveniles migrate to the eastern Pacific Ocean (EPO), where they remain for several months, or longer, and the.n return to the WPO. Lengthfrequency and tagging data show that many bluefin arrive in the EPO as 1-and 2-year olds, and remain there for one or two fishing seasons before returning to the WPO. The proportion of the fish which make the west-to-east migration varies among years. The numbers of 1-, 2-, 3-, 4, and >4 –year olds in the catches of the EPO are estimated for most years of the 1952-1991 period. SPANISH: EI desove del atun aleta azul del norte del Pacifico, Thunnus thynnus, ocurre solamente en el Océano Pacifico occidental (WPO), pero números substanciales de los juveniles migran al Océano Pacifico oriental (OPO), donde permanecen unos meses, 0 mas, antes de regresar al WPO. Datos de marcado y frecuencia de talla indican que muchos aletas azules llegan al OPO a 1 o 2 anos de edad, y permanecen alIi una 0 dos temporadas de pesca antes de regresar al WPO. La proporcion de los peces que migra del oeste al este varia entre anos. Se estima el numero de peces de 1, 2, 3, 4, Y>4 anos de edad en las capturas del OPO para la mayoria de los anos del periodo de 1952-1991. (PDF contains 40 pages.)

An evaluation of length-frequency sampling procedures and subsequent data analysis for purse seine-caught yellowfin tuna in the Eastern Pacific Ocean

ENGLISH: A two-stage sampling design is used to estimate the variances of the numbers of yellowfin in different age groups caught in the eastern Pacific Ocean. For purse seiners, the primary sampling unit (n) is a brine well containing fish from a month-area stratum; the number of fish lengths (m) measured from each well are the secondary units. The fish cannot be selected at random from the wells because of practical limitations. The effects of different sampling methods and other factors on the reliability and precision of statistics derived from the length-frequency data were therefore examined. Modifications are recommended where necessary. Lengths of fish measured during the unloading of six test wells revealed two forms of inherent size stratification: 1) short-term disruptions of existing pattern of sizes, and 2) transition zones between long-term trends in sizes. To some degree, all wells exhibited cyclic changes in mean size and variance during unloading. In half of the wells, it was observed that size selection by the unloaders induced a change in mean size. As a result of stratification, the sequence of sizes removed from all wells was non-random, regardless of whether a well contained fish from a single set or from more than one set. The number of modal sizes in a well was not related to the number of sets. In an additional well composed of fish from several sets, an experiment on vertical mixing indicated that a representative sample of the contents may be restricted to the bottom half of the well. The contents of the test wells were used to generate 25 simulated wells and to compare the results of three sampling methods applied to them. The methods were: (1) random sampling (also used as a standard), (2) protracted sampling, in which the selection process was extended over a large portion of a well, and (3) measuring fish consecutively during removal from the well. Repeated sampling by each method and different combinations indicated that, because the principal source of size variation occurred among primary units, increasing n was the most effective way to reduce the variance estimates of both the age-group sizes and the total number of fish in the landings. Protracted sampling largely circumvented the effects of size stratification, and its performance was essentially comparable to that of random sampling. Sampling by this method is recommended. Consecutive-fish sampling produced more biased estimates with greater variances. Analysis of the 1988 length-frequency samples indicated that, for age groups that appear most frequently in the catch, a minimum sampling frequency of one primary unit in six for each month-area stratum would reduce the coefficients of variation (CV) of their size estimates to approximately 10 percent or less. Additional stratification of samples by set type, rather than month-area alone, further reduced the CV's of scarce age groups, such as the recruits, and potentially improved their accuracy. The CV's of recruitment estimates for completely-fished cohorts during the 198184 period were in the vicinity of 3 to 8 percent. Recruitment estimates and their variances were also relatively insensitive to changes in the individual quarterly catches and variances, respectively, of which they were composed. SPANISH: Se usa un diseño de muestreo de dos etapas para estimar las varianzas de los números de aletas amari11as en distintos grupos de edad capturados en el Océano Pacifico oriental. Para barcos cerqueros, la unidad primaria de muestreo (n) es una bodega de salmuera que contenía peces de un estrato de mes-área; el numero de ta11as de peces (m) medidas de cada bodega es la unidad secundaria. Limitaciones de carácter practico impiden la selección aleatoria de peces de las bodegas. Por 10 tanto, fueron examinados los efectos de distintos métodos de muestreo y otros factores sobre la confiabilidad y precisión de las estadísticas derivadas de los datos de frecuencia de ta11a. Se recomiendan modificaciones donde sean necesarias. Las ta11as de peces medidas durante la descarga de seis bodegas de prueba revelaron dos formas de estratificación inherente por ta11a: 1) perturbaciones a corto plazo en la pauta de ta11as existente, y 2) zonas de transición entre las tendencias a largo plazo en las ta11as. En cierto grado, todas las bodegas mostraron cambios cíclicos en ta11a media y varianza durante la descarga. En la mitad de las bodegas, se observo que selección por ta11a por los descargadores indujo un cambio en la ta11a media. Como resultado de la estratificación, la secuencia de ta11as sacadas de todas las bodegas no fue aleatoria, sin considerar si una bodega contenía peces de un solo lance 0 de mas de uno. El numero de ta11as modales en una bodega no estaba relacionado al numero de lances. En una bodega adicional compuesta de peces de varios lances, un experimento de mezcla vertical indico que una muestra representativa del contenido podría estar limitada a la mitad inferior de la bodega. Se uso el contenido de las bodegas de prueba para generar 25 bodegas simuladas y comparar los resultados de tres métodos de muestreo aplicados a estas. Los métodos fueron: (1) muestreo aleatorio (usado también como norma), (2) muestreo extendido, en el cual el proceso de selección fue extendido sobre una porción grande de una bodega, y (3) medición consecutiva de peces durante la descarga de la bodega. EI muestreo repetido con cada método y distintas combinaciones de n y m indico que, puesto que la fuente principal de variación de ta11a ocurría entre las unidades primarias, aumentar n fue la manera mas eficaz de reducir las estimaciones de la varianza de las ta11as de los grupos de edad y el numero total de peces en los desembarcos. El muestreo extendido evito mayormente los efectos de la estratificación por ta11a, y su desempeño fue esencialmente comparable a aquel del muestreo aleatorio. Se recomienda muestrear con este método. El muestreo de peces consecutivos produjo estimaciones mas sesgadas con mayores varianzas. Un análisis de las muestras de frecuencia de ta11a de 1988 indico que, para los grupos de edad que aparecen con mayor frecuencia en la captura, una frecuencia de muestreo minima de una unidad primaria de cada seis para cada estrato de mes-área reduciría los coeficientes de variación (CV) de las estimaciones de ta11a correspondientes a aproximadamente 10% 0 menos. Una estratificación adicional de las muestras por tipo de lance, y no solamente mes-área, redujo aun mas los CV de los grupos de edad escasos, tales como los reclutas, y mejoró potencialmente su precisión. Los CV de las estimaciones del reclutamiento para las cohortes completamente pescadas durante 1981-1984 fueron alrededor de 3-8%. Las estimaciones del reclutamiento y sus varianzas fueron también relativamente insensibles a cambios en las capturas de trimestres individuales y las varianzas, respectivamente, de las cuales fueron derivadas. (PDF contains 70 pages)

Length weight relationship, condition factors and fecundity of Chrysichthys nigrodigitatus and Chrysichthys walkeri in Asejire Lake

Sex ratio and fecundity variations of Chrysichthys nigrodigitatus and Chrysichthys walkeri from Asejire Lake (Nigeria) were examined. The Logarithm transformation of weight (W) against standard length (SL) gave a straight-line graph represented by the following equations: 1) C. nigrodigitatus LogW =-0.66 + 2.13 Log SL; = 0.854; (P < 0.001) n = 209; 2) C. walkeri LogW = -1.23 + 2.63 Log SL; = 0.759; (P < 0.001) n = 237. Males were generally more than females in both species. The ratio of males:females was higher in C. nigrodigitatus (1:0.18) than in C. walkeri (1:0.8). C. walkeri attained sexual maturity at a smaller size of 20.0 g (12.0 cm Standard Length) compared with C. nigrodigitatus maturity size of 45.0 g (14.0 cm Standard Length). Relative fecundity was not dependent on body weight and standard length for C. walkeri but it was significant at P < 0.05 and P < 0.01 respectively for C. nigrodigitatus

Aspects of the reproductive biology of Mugil cephalus (Linnaeus, 1857) in Bonny Estuary

Aspects of the reproductive biology of Mugil cephalus in the Bonny estuary (Nigeria) were studied between January and December 1996. Males were observed to be more slender than females while the females have deeper bodies. The male:female ratio (1:0:95) was not significantly different. The minimum size at maturity was 16.6cm (0.5 yr). Fish matured at 24.3cm TL(1.76 yr) with median maturity size of 19.5cm TL(0.71 yr). Median maturity for male and female fish were 16.4cm TL(0.41 yr) and 18.2cm TL(0.60 yr) respectively. Breeding occurred once a year between September and December, from late rainy season to early dry season. Mean absolute fecundity was 1,403, 808 eggs (range 107, 729-4,445, 423 eggs) for fish of 17.0.29.5cm TL (mean 22.5cm TL). Fecundity correlated positively with fish total weight, length, ovary weight and age

The reproduction of Oreochromis niloticus (Linnaeus) in Opa reservoir, Ile-Ife, Nigeria

Oreochromis niloticus is one of the commercial fish species in Opa reservoir. It bred throughout the period of study in the reservoir. The fish species is a maternal mouth brooder with the female specimens carrying eggs and alevins in their mouths. The sex ratio of O. niloticus was 1:1 and the maximum fecundity recorded was 1810 eggs. The fecundity increased as the fish length increased. The relatively high fecundity of the fish species in the reservoir is an indication of the suitability of the small reservoir in contributing to fish production

Vergleich von Ausbeutefaktoren und Eislagerqualität zwischen Kliesche (Limanda limanda) und Scholle (Pleuronectes platessa) aus der Nordsee

North Sea plaice (Pleuronectes platessa) and dab (Limanda limanda) were experimentally stored in ice for 6 days during the 181th cruise of the FRV “Wather Herwig III”. It could be demonstrated that both flat fish species showed the same storage properties and were of a comparable quality until the end of the storage experiment. The quality of both species was determined by sensory assessment of the quality grade, by measuring of the impedance using the German Fischtester VI and the Icelandic RT- tester and pH- and TVB- N- measurements. The average length of North Sea dab is generally small (female: 18,5 ± 3,9 cm; male: 17 ± 2,9 cm), therefore it seemed to be more efficient to process fish portions (eviscerated, head, tail, fins and part of belly flaps removed). The yield by manually processed filets or fish portions from dab is about 30 or 62 %, respectively

Length-weight relationship and organ indices of pond raised and wild population of C. gariepinus (Burchell 1822) pisces-Claridae

Samples of C. gariepinus collected from the wild and cultured populations in Plateau and Niger States of Nigeria were analyzed for length-weight relationship and organ indices (Gonadosomatic index (GSI), hepatosomatic index (HSI), renalsomatic index (RSI) and somatic fat deposit index (PDI). High correlation and linear relationship between body length and body weight was observed in all sample population (P<0.05). A significant difference was observed between the GSI of males and females of both wild and cultured population and also between females of the wild and cultured population,(P < 0.05).There was no significant difference in HSI, CSI RSI and PDI of all the sample populations (P < 0.05).The importance of length-weight relationship and organ indices in fish production are discussed

Growth response and survival of F1 hybrid fry of Heterobranchus longifilis and Clarias gariepinus reared in glass aquaria and plastic basins

The growth response of F1 hybrid fry of female Heterobranchus longifilis and male Clarias gariepinus were investigated under laboratory conditions in glass aquaria glass tanks and plastic basins. The larvae were produced artificially after inducement with Ovarptim. The hatching percentage was very high. Weekly mean length and weight were monitored for 6 weeks. The average length increase was higher in aquaria glass tanks than in plastic basins. However, there were depressed and irregular weight increases in both types of rearing troughs while significant weight increase (P<0.05) was recorded at week 6 in the plastic basin. Generally, the growth rate and survival in both containers were not significantly different

Fishery resource surveys: beyond length-weight relationship models

Fisheries resource surveys are regular management tools for rational exploitation of commercial fisheries. In a growing number of cases, the use of these resource surveys has been largely restricted to assessment of the relative well being of fish stocks and the potential yields of such fisheries. This paper seeks to demonstrate that the data from such surveys can also be easily used to evaluate species diversity of such fisheries, both in terms of species richness and equitability of distribution. Using published data on two freshwater and two marine fisheries as case studies, Shannon-Wiener Diversity Function and Simpson's Index were computed for each of these fisheries. These biodiversity indices gave a deeper insight into the environmental status of each of these fisheries, beyond what the length-weight relationship models can reveal. Generally, while the marine fisheries showed more species richness, the freshwater fisheries apparently had more stable and equilibrated fish communities