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Strain Crossing in Mrigal (cirrhinus Cirrhosus): an Avenue to Persuade Heterosis in F1 Generation of Wild×hatchery Hybrid

Md. Ashkar Bin Sayeed
Fisheries and Marine Resource Technology Discipline, Life Science School, Khulna University, Khulna 9208, Bangladesh

Abstract/ Executive Summary:

While the increase of the yield of commercially trendy farmed fishes are of special priority in aquaculture, a number of handy technologies are indispensable to realize the surplus production aiming to feed the growing population. As a genetic means of doing this, hybridization technology has been being used for years, because it can produce hybrid vigor through inducing heterosis. Similar attempt was made in mrigal, Cirrhinus cirrhosus, by crossing the hatchery strain with the riverine strain to investigate the heterotic effect in the progeny the species could generate through such intra-specific hybridization. Mean fertilization and hatching rates in hybrids were found to be lower by 7% and 4% respectively than that in purebreds, which envisioned to be trivial to impact the purpose of crossing. Comparative growth test between purebreds and hybrids showed significant differences (p< 0.05) in weight and length, and resulted 30.51% heterosis in hybrid mrigal. This experiment can be considered as a preliminary investigation to motivate the application of strain crossing in mrigal farming and the result found thereof can be used as a clue to optimize this growth boosting technique for the species through further research.

Keywords: Aquaculture genetics, Intra-specific hybridization, Mrigal, Heterosis, Hybrid vigor

Location: Khulna, Bangladesh

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Carp fish

Objectives:

To motivate the application of strain crossing in mrigal farming and the result found thereof can be used as a clue to optimize this growth boosting technique for the species through further research.

Methodology:

Design of experiment: The experiment was designed to conduct at two distinct phases viz, induced breeding with reciprocal hybridization (riverine strain × hatchery strain) and comparative growth test of the hybrids with the parents. Fertilization and hatching rates of control and treatment groups were determined and the hatchlings were reared up to 10 weeks in earthen ponds for subsequent growth test. Collection, transportation and maintenance of broodstock: Broodstocks of riverine (Padma) strain were collected from Freshwater Research Sub-station, Jessore and those of hatchery strain were sourced from Fish Seed Multiplication Center, Khulna. A total of five pairs of brood from each source were carried to the study site (Khulna) in large plastic containers having arrangements of ice, saline and aeration for expedient transportation. Reaching at experimental station the broods were allowed for a temporary rest in large concrete tanks set under water cascade and after that tagged and released in brood rearing ponds. Supplementary feed was given at a rate of 5% of total biomass. Induced breeding with hybridization: The matured brood fishes were prepared for hypophysation keeping them under a 12-hour photoperiod in conditioning tank. Shifting in brood tank, the induced breeding was performed by injecting carp PG hormone intramuscularly. Dry PG was crushed, dissolved and centrifuged for collecting its supernatant solution, which was then taken for the injection. The sex ratio of the spawners at ‘1 (male) : 2 (female)’ was maintained. Female broods were treated with a double dose of 2 and 6 mg PG per kg body weight at 6 hours interval while male broods were given a single dose of 2 mg PG per kg body weight at the time of second administration to the female. The stripping was done by applying gentle downward pressure with the thumb and index fingers from just below the pectoral fins up to the genital opening of the fish. Eggs and milt thus collected were mixed well for proper fertilization. A reasonable amount of physiological saline solution (5% dextrose and 0.9% NaCl) was used during fertilization to increase the viability of eggs and sperm and also to reduce the stickiness of the eggs. For heterosis production and analysis, two different strains of mrigal were reciprocally hybridized. For this, the artificial inseminations were carried out by Riverine ?× Riverine ? and Hatchery ?× Hatchery ? as control and by Riverine ?× Hatchery ? and Riverine ?×Hatchery ?as treatment. Fertilization and hatching rates: The inseminated eggs were then transferred into four incubation tanks of 50 liter water holding capacity connected to water circulating system to facilitate gentle movement of the developing eggs at all times for proper hatching. Fertilization rates were then determined as: Fertilization rate (%) = (Number of fertilized eggs having transparent shells present in a specific volume of water taken for measurement / Number of total eggs present in that volume) * 100. After passing the hatching period of about 24 hours, hatching rates were calculated in similar way as: Hatching rate (%) = (Number of hatchlings ascertained by visual observation and present in a specific volume of fertilized eggs set for measurement / Number of total fertilized eggs present in that volume) * 100. Culture for growth test: Three days old hatchlings were transferred into eight prepared earthen ponds [for 2 strains × 2 observations (1 control and 1 treatment) × 2 replications of each] and reared for ten weeks. Pond preparation, liming, fertilization, acclimatization, stocking, feeding, water quality maintenance etc. were done according to local standard aquaculture practice. Growth in terms of weight and length were checked at every tenth day through random sampling and recorded for subsequent analyses. Heterosis calculation and statistical analysis: Heterosis thus produced in the hybrids of the mrigal was measured from a comparative growth test with the parents and its effect was calculated as: Heterosis (%) = (Mean growth of F1 reciprocal hybrids – Mean growth of parents) * 100. The results of the various growth trials were statistically compared by One-way ANOVA and using R Programming Language.

Source of Information: Journal of Fisheries Volume 3 Issue 2 Pages: 245-250 August 2015

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Hybrid of two strains of the same species sourced from different or even distant population often had a higher growth rate than the offspring of either parental strain; this fact was proved by lots of experiments in various fish species worldwide. Similar upshot was evidenced in the current study where the strain-crossed mrigal demonstrated positive heterosis (30.51%) in growth performance. Difference in average fertilization and hatching rates between purebreds and hybrids were too trifling to impede the research target. Hence, the current result concludes the importance of practicing intraspecific strain crossing in mrigal as to be promising for its stock improvement and commercial farming in the locality. Even this prefatory study motivates the application of strain crossing in mrigal culture and offers a hint to optimize this yield raising technique for the species through further research.

Knowledge Management: Journal